CH 4
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4.1 True/false statements
True/false statements
Logic
is the ±eld of precise reasoning. If people under age 7 can't ride, and Jan is under age 7, then Jan
can't ride. That's logic in action.
At the heart of logic are true/false statements
, which are statements that are either true or false, such as
"Jan is under age 7." The truth value
of a true/false statement indicates whether the statement is true or
false based on the data or facts given. Given the fact that Jan was born 8 years ago, the truth value of the
statement "Jan is under age 7" is false. Logic builds on such true/false statements and truth values.
PARTICIPATION
ACTIVITY
4.1.1: True/false statements and truth values.
PARTICIPATION
ACTIVITY
4.1.2: True/false statements.
Indicate whether the statement is a true/false statement.
1)
Joe passed Chem101.
Yes
No
2)
Joe can take Chem102.
Yes
No
Animation content:
unde±ned
Animation captions:
1. Logic starts with statements that are either true or false. Ex: "Lee passed Chem101" must be
true or false. If Lee got a B: true. If an F: false. If Lee didn't take the class: false.
2. "Mia is a parent" is a true/false statement, because the statement is either true or false. If Mia
has no kids, the statement is false. Later, if Mia has 3 kids, the statement is true.
3. "Good morning" is not a true/false statement, as no truth value exists for such a greeting. "What
day is today?" is not a true/false statement either, instead being a question.
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3)
Joe is a parent.
Yes
No
4)
Are the kids sleepy?
Yes
No
5)
Hello everybody.
Yes
No
6)
Kay does not have ID.
Yes
No
7)
Kay might win the lottery.
Yes
No
8)
The earth is ²at.
Yes
No
PARTICIPATION
ACTIVITY
4.1.3: Truth value of true/false statements.
For given facts, a true/false statement's truth value is either true or false. For the facts given
below, indicate whether the subsequent true/false statement's truth value is true or false.
1)
Fact: Stacy got a B in Chem101.
Statement: Stacy passed Chem101.
True
False
2)
Fact: Stacy got an F in Chem101.
Statement: Stacy passed Chem101.
True
False
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3)
Fact: Mia has three children.
Statement: Mia is a parent.
True
False
4)
Fact: Mo is 5 years old.
Statement: Mo is at least 4 years old.
True
False
5)
Fact: Ladybugs can't bite people.
Statement: A ladybug can bite people.
True
False
6)
Fact: Today is Monday.
Statement: A week has 7 days.
True
False
Does your dog bite?
Just for fun, this classic scene (77 sec) from an early Pink Panther movie shows a
misunderstanding around the truth value of a true/false statement "My dog does not
bite". The dog part starts at 50 sec.
The negation of a true/false statement
People apply logic in everyday life. A common logic task is to negate
a true/false statement, or to change
the statement so that the truth value is reversed. Unfortunately, the nature of English can lead to mistakes.
In everyday life, people don't say "Not Mia is a parent" but rather "Mia is not a parent", so negation in English
is harder. To avoid mistakes, logicians use letters like P, so the negation of P is "NOT P".
Photo source: Screenshot from the above video clip on youtube.com, 2019.
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PARTICIPATION
ACTIVITY
4.1.4: The negation of a true/false statement.
PARTICIPATION
ACTIVITY
4.1.5: Expressing in English that a true/false statement is false.
Choose the most appropriate negation of the true/false statement.
1)
Joe broke the theft law.
Joe did not break the theft law.
No person broke the theft law.
Joe broke no laws.
2)
Cleo is barking.
Cleo is quiet.
Cleo is not barking.
3)
The package has been opened.
The package is unopened.
The package has not been
touched.
The package is wide open.
PARTICIPATION
ACTIVITY
4.1.6: Selecting a good negation of a true/false statement.
Indicate whether the negation is good or poor.
Animation content:
unde±ned
Animation captions:
1. "Mia is a parent" is a true/false statement. Logicians use letters for such statements, like P. If P
is true, then the negation NOT P is false.
2. Unfortunately, people can't use the same approach for the negation in regular English. Nobody
says "Not Mia is a parent", but instead "Mia is not a parent".
3. Such negation in English is prone to errors. The negation of "Jan is under age 7" is "Jan is 7 or
older", rather than "Jan is over age 7", because Jan can be 7.
4. The negation of "The food is expensive" should not be "The food is cheap" because the meaning
may change (cheap implies bad). A better negation is "The food is inexpensive".
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1)
Statement: The player is under 10 years
old.
Negation: The player is over 10 years
old.
Good
Poor
2)
Statement: Mo is short.
Negation: Mo is tall.
Good
Poor
3)
Statement: Jan is a fast worker.
Negation: Jan is a slow worker.
Good
Poor
4)
Statement: The babysitter is reliable.
Negation: The babysitter is unreliable.
Good
Poor
PARTICIPATION
ACTIVITY
4.1.7: Common survey errors involving negating.
Logic mistakes commonly appear in surveys. Indicate whether the pair of choices are good or
poor, based on whether the second choice is a good negation of the ±rst.
1)
Choice 1: I work less than 20 hours per
week.
Choice 2: I work more than 20 hours per
week.
Good
Poor
2)
Choice 1: I am currently employed by
the government.
Choice 2: I am not currently employed
by the government.
Good
Poor
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3)
Choice 1: The exam was easy.
Choice 2: The exam was hard.
Good
Poor
So you think I'm fat?
People commonly make logical negation errors in everyday life, especially on subjects to
which the person is sensitive. How often has one observed things similar to the
following?
Do you think I look skinny? No? So you think I'm fat?
Am I overdressed? No? So you think I'm underdressed?
I asked the manager if Kia was a strong worker and she said no. So maybe we
should let Kia go, as we don't want weak workers.
News story: "Stocks are not expected to rise." Person talking to a friend: "The news
said stocks are expected to fall".
That car is not rated as highly reliable. I don't think you should buy that car,
because you don't want a car that is unreliable.
My son didn't call to wish me happy birthday. He must not care about me.
Many everyday problems occur due to incorrectly negating.
Garth knows how to negate.
Garth from the Saturday Night Live recurring sketches about Wayne's World knows how
to negate accurately. Garth just says "I'm having a good time ... NOT", as in this 10-sec
video
. That works! Too bad using that approach in real life is not socially acceptable.
Photo source: Screenshot from above youtube video, 2019.
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CHALLENGE
ACTIVITY
4.1.1: True/false statements.
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Start
2
3
Indicate whether the statement is a true/false statement:
How are you doing?
Check
Next
4.2 If-then statements
If-then statements
One form of logic uses an if-then statement
: A statement relating two true/false statements, saying that IF
statement 1 is true, THEN statement 2 is also true.
PARTICIPATION
ACTIVITY
4.2.1: An if-then statement relates two true/false statements: If statement1 is
true, then statement2 is also true.
Animation content:
unde±ned
Animation captions:
1. An if-then statement relates two true/false statements: If statement 1 is true, then statement 2
is also true.
2. Lee got a B in Chem101. Because "Lee passed Chem101" is true, then "Lee can take Chem102"
is also true, according to the if-then statement.
3. When statement 1 is false, the if-then statement says nothing about statement 2's truth value.
Maybe Lee can still take Chem102 with instructor permission, by passing a test, etc.
1
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PARTICIPATION
ACTIVITY
4.2.2: If-then statements.
Indicate whether "Bandit will bark" (Bandit is a dog) is known to be true, based solely on the
info given and this if-then statement:
If Bandit is scared, then Bandit will bark.
1)
"Bandit is scared" is true.
True (Bandit will bark)
False (Bandit will not bark)
Unknown (whether Bandit will or
will not bark)
2)
Keesha scared Bandit.
True (Bandit will bark)
False (Bandit will not bark)
Unknown
3)
"Bandit is scared" is false.
True (Bandit will bark)
False (Bandit will not bark)
Unknown
Confusing terminology can slow learning.
The ±eld of logic uses different terms than in this material:
A true/false statement is called a proposition
.
An if-then statement is called a logical implication
.
But, those words have different meanings in everyday English, where a "proposition" is a
suggestion like "I think we should get married", and an "implication" is something that can
be concluded indirectly as in "His sloppy appearance implies he doesn't want this job."
Just as in the math and statistics ±elds, the logic ±eld's rede±ning of common words can
cause confusion and slow the learning of concepts. So, this material uses more intuitive
terms. If studying formal logic further, the reader will want to learn the ±eld's more
common terms.
Everyday if/then statements
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If-then statements appear in everyday life, even if not always written in if-then form.
PARTICIPATION
ACTIVITY
4.2.3: If-then statements in everyday life.
PARTICIPATION
ACTIVITY
4.2.4: Detecting if-then statements from English sentences.
Indicate the most appropriate if-then statement that the English sentence represents.
1)
If Cleo sees a stranger, Cleo will bark.
If Cleo sees a stranger, then Cleo
will bark.
If Cleo barks, then the Cleo saw a
stranger.
2)
Travelers not present 45 min before
scheduled departure are subject to loss
of seat.
If a traveler isn't present 45 min
before scheduled departure, then
the traveler is subject to loss of
seat.
If a person's seat was lost, then
the traveler was not present 45
min before scheduled departure.
Animation content:
unde±ned
Animation captions:
1. If-then statements are common in everyday life. A hotel policy may state: If you cancel by 6 pm,
you will not be charged. The "then" before "you will not" is understood.
2. Often statements are written differently, as in: Cancellations made by 6 pm will not be charged.
Or perhaps: You will not be charged if you cancel by 6 pm.
3. A country may state this if-then statement in various ways: If you don't have a passport, you will
be denied entry. The ability to mentally derive the if-then statement logic is useful.
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3)
A package cannot be returned if the
package has been opened.
If a package cannot be returned,
then the package was opened.
If a package has been opened,
then the package cannot be
returned.
If a package has not been
opened, then the package can be
returned.
4)
A free kick is awarded when a player
trips an opponent.
If a player trips an opponent, then
a free kick is awarded.
If a free kick is awarded, then a
player tripped an opponent.
CHALLENGE
ACTIVITY
4.2.1: If-then statements.
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Start
2
3
4
Based on the following correct if-then statement and given fact, select whether the last statement is true, false, or unknown.
If the weather is rainy, then the garden does not need to be watered.
Fact: The weather is not rainy.
Statement: The garden does not need to be watered.
Check
Next
4.3 Logical deduction
1
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Logical deduction
Perhaps the best-known form of logic is logical deduction
, or using one statement's truth value to
determine another statement's truth value. Given a correct if-then statement, if statement 1 is true, then a
person can deduce that statement 2 is true. Interestingly, if statement 2 is false, then a person can also
deduce that statement 1 is false.
PARTICIPATION
ACTIVITY
4.3.1: If-then statements and logical deduction.
PARTICIPATION
ACTIVITY
4.3.2: Basic deduction from an if-then statement.
Given the if-then statement: If A, then B. What can be deduced?
1)
A is true, so B is true.
Yes
No
2)
A is false, so B is false.
Yes
No
Animation content:
unde±ned
Animation captions:
1. Logical deduction involves determining one true/false statement's truth value from another
statement's true value. If A is true, then B is true.
2. Given the statement: If Pat just drove the car, then Pat's engine is hot. Given data that Pat just
drove the car is true, then Pat's engine is hot is also true. That's logical deduction.
3. But, if "Pat just drove the car" is false, nothing is known about the engine being hot. Maybe
somebody else drove heated the engine, or not so the engine is cold.
4. Interestingly, if the engine is NOT hot, then Pat certainly did NOT just drive the car. (If Pat had
just driven, the engine would be hot). That's also logical deduction.
5. In other words, given "If A, then B", if data shows B is false, then A is also false.
³. But, given that the engine is hot, nothing is known about whether Pat just drove the car.
Somebody clearly drove, but who is unknown.
7. In summary, given "If A, then B", A is true means B is true, and B is false means A is false. Both
are logical deductions. For the other two cases, nothing can be deduced.
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3)
B is false, so A is false.
Yes
No
4)
B is true, so A is true.
Yes
No
PARTICIPATION
ACTIVITY
4.3.3: Did Pat just drive the car?
A police o´cer investigates a hit-and-run. Somebody says they saw Pat's car leaving the hit-
and-run scene, so the o´cer goes to Pat's home, just 10 minutes after the hit-and-run.
Consider the correct if-then statement: If Pat was just driving, then Pat's engine is hot.
1)
Pat says "I've been home all day. Go feel
my car's engine; if the engine is cool,
you know I wasn't just driving the car." Is
Pat's logic correct?
Yes
No
2)
The o´cer feels Pat's car engine, which
is hot. The o´cer says "The engine is
hot, so you were just driving." Is the
o´cer's logic correct?
Yes
No
PARTICIPATION
ACTIVITY
4.3.4: Uses of logical deduction.
Which are proper applications of logical deduction?
1)
Everyone agrees that if Val robbed a
house last night, then Val must have
been in that house last night. To prove
Val did not rob the house, Val's defense
attorney seeks to prove Val was not in
the house last night.
OK
Not OK
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2)
Everyone agrees that if Val robbed a
house last night, then Val must have
been in that house last night. To prove
Val robbed the house, a prosecutor
seeks only to prove Val was in the
house last night.
OK
Not OK
Chained deductions
People commonly make deductions by chaining several if-then statements.
PARTICIPATION
ACTIVITY
4.3.5: Chained deductions.
PARTICIPATION
ACTIVITY
4.3.6: Chained deductions.
Consider the example above, which includes the if-then statements "If A, then B" and "If B, then
C".
1)
If A is true, can one deduce that C is
true?
Yes
No
Animation content:
unde±ned
Animation captions:
1. Given "If A, then B" plus "If B, then C", and fact "A is true". Then B must be true. Since B is true,
then C must be true. People commonly make such chained deductions.
2. Or, given that C is false, one can deduce that B is false, and then deduce that A is false.
3. If Jo has a license, then Jo is over 15, and so then Jo can enter. Checking Jo's date of birth on
the license is not necessary.
4. Given that Jo was too young to enter, then Jo is not over 15, so then Jo cannot have a driver's
license.
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2)
If A is false, can one deduce that C is
false?
Yes
No
3)
If B is false, can one deduce that A is
false?
Yes
No
4)
If B is false, can one deduce that C is
false?
Yes
No
5)
If C is true, can one deduce that A is
true?
Yes
No
Witches and chained deductions.
This classic Monty Python movie scene (2 min) shows particularly erroneous chained
logical deductions.
CHALLENGE
ACTIVITY
4.3.1: Logical deduction.
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Photo from video clip of the movie "Monty Python and the Holy Grail", taken from above link.
Start
Given: If A, then B. ©zyBooks 11/03/23 16:51 1490122
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2
Indicate what is known for the given data: B is true.
A is
Check
Next
4.4 If-then statements whose reverse is correct
If-then statements whose reverse is correct too
Sometimes an if-then statement works not just forwards but also in reverse, meaning that both "If A, then B"
and "If B, then A" are correct. An if-then statement whose reverse is also correct allows a person to deduce
more than just a one-way if-then statement.
PARTICIPATION
ACTIVITY
4.4.1: If-then statements whose reverse is correct.
Note: Logicians indicate if-then statements whose reverse is also correct by saying "A if and only if B", or "A
iff B" for short. Logicians write a regular if-then statement using the notation A →
B, and an if-then
statement whose reverse is correct as A ↔
B.
Animation content:
unde±ned
Animation captions:
1. An if-then statement only allows deduction when A is true, not false. When A is true, then B
must be true. When A is false, the statement says nothing about B.
2. Given: If Bandit is scared, Bandit will bark. But when Bandit isn't scared, nothing can be deduced
about barking. Bandit might bark anyway if angry or excited.
3. Also, if B is known to be false, then A can be deduced to be false. But, B being true doesn't mean
A is true.
4. However, for some if-then statements, the reverse is also correct. Correct: If today is Mon, then
tomorrow is Tue. Also correct: If tomorrow is Tue, then today is Mon.
5. For such a case, B can ONLY be true if A is true. If A is false, B must be false. And, if B is true, A
must be true.
1
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In everyday English, sometimes people will say something like "If A, then B, and vice-versa", as in "Those
twins are something. If Jo cries, then Kay cries, and vice-versa." However, in everyday English, people often
just state the forward if-then, with the reverse being understood using common sense. That situation can
unfortunately cause confusion, but English isn't perfect.
Logic requires focus
A note to readers: Understanding logic requires a lot of mental focus. If the reader has
been enjoying music (or maybe even YouTube videos) while learning material in earlier
chapters, the reader is encouraged to turn the music off for a while, and really let the
brain focus on the logic. The reader may ±nd that exercise challenging and fun.
PARTICIPATION
ACTIVITY
4.4.2: Determining the truth value of a forward conditional statement and the
converse.
Use everyday knowledge to determine whether the conditional statement is only true forward,
or if the converse is also true too.
1)
If rain is falling, then the sky has clouds.
Forward only
Forward and converse
2)
If today is Saturday, then today is the
weekend.
Forward only
Forward and converse
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3)
If smoke exists near a smoke detector,
then a functioning smoke detector will
sound.
Forward only
Forward and converse
4)
If a lamp is unplugged, then the lamp
will not light.
Forward only
Forward and converse
5)
If a car was recently running, then the
engine will be hot.
Forward only
Forward and converse
6)
A de±nition of shoplifting is a person
intentionally removing an item from a
store without paying. Stated as a
conditional statement: If a person
intentionally removes an item from a
store without paying, that person has
committed shoplifting.
Forward only
Forward and converse
A note to readers: For nearly any example above, some readers will ±nd an exception. Maybe an unplugged
lamp will light via an internal battery. Maybe a smoke detector will sound due to malfunctioning. Maybe
once in history the day after Monday wasn't Tuesday because the government adjusted the calendar (
that
really happened
). The reader is asked, for this section and others, to assume the common sense situation
applies. Otherwise, logic has to be taught mostly using symbols like A and B, but this material strives to
teach logic in context of everyday life.
Logical deduction with if-then statements whose reverse is correct
As seen in the animation above, an if-then statement whose reverse is correct allows for more deductions.
In a if-then statement "If A, then B" whose reverse is correct, both A and B must be true, or both must be
false. So knowing the truth value of either A or of B, a person can deduce the other.
PARTICIPATION
ACTIVITY
4.4.3: Deducing from if-then statements when given that the reverse is correct.
Given: For each if-then statement below, the reverse is also correct.
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1)
If A, then B.
A is true. So B is ___.
true
false
2)
If A, then B.
A is false. So B is ___.
true
false
3)
If A, then B.
B is true. So A is ___.
true
false
4)
If A, then B.
B is false. So A is ___.
true
false
5)
If a baby needs something, a baby cries.
The baby is crying. So the baby ___
something.
needs
may need
CHALLENGE
ACTIVITY
4.4.1: If-then statements whose reverse is correct.
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Start
2
3
4
5
Using everyday knowledge, indicate whether the if-then statement's reverse is also correct.
X: If rain is falling, then the sky has a cloud.
Y: If Jo is taller than Lee, then Lee is shorter than Jo.
X is
Y is
1
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Check
Next
A correct if-then statement is: If today is Monday, then tomorrow is Tuesday.
An incorrect if-then statement is: If today is Monday, then tomorrow is Friday.
4.5 Common logical deduction mistakes
Incorrect if-then statements
A common logic-related mistake is to start from an incorrect if-then statement. An if-then statement like "If
A, then B" might be said to be correct
if A being true indeed means B is also true.
Most incorrect cases aren't as obvious.
"If an employee is often late to work, then the employee must be irresponsible." But, maybe the
employee is visiting an ill parent in the mornings, and working late to make up the time? Interestingly,
this error of attributing behavior to character ²aws instead of external situations is so common as to
be known as the fundamental attribution error
.
"If a poorly-dressed person is lying on the sidewalk, then the person is homeless." Many people make
that assumption, which is often correct. But maybe the person was heading to work, fell ill, and needs
help? This video (3-min) shows an experiment where people didn't help a person lying on the sidewalk,
except when the person was dressed well.
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PARTICIPATION
ACTIVITY
4.5.1: Correct and incorrect if-then statements.
Indicate which if-then statements are most likely to be correct or incorrect.
1)
If a car won't start, something is wrong
with the car.
Correct
Incorrect
2)
If a new coworker doesn't smile when
introduced, the coworker is unfriendly.
Correct
Incorrect
3)
If I don't get a call from my adult child
on my birthday, then my child no longer
cares about me.
Correct
Incorrect
4)
If my neighbor says my haircut looks
great, then my neighbor thinks my hair
looked bad before.
Correct
Incorrect
Photo taken from above video link on youtube, 2019
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If Mia has at least one kid, then Mia is a parent / If Mia is a parent, then Mia has at least one kid
If today is Monday, then tomorrow is Tuesday / If tomorrow is Tuesday, then today is Monday
5)
If my spouse isn't saying much during
this car drive, then my spouse must be
upset with me.
Correct
Incorrect
6)
If Jo babysits, Pat will pay Jo. Given this
info: Jo did babysit but Pat did not pay
Jo..
Correct
Incorrect
Note that an if-then statement is itself a true/false statement. So an incorrect if-then statement is like a
true/false statement with a truth value of false. This concept can be a little hard to get one's head around,
so this material won't discuss that point further.
Common logic mistake: Assuming if-then applies in both directions
In everyday life, many if-then statements have a reverse that is also correct, as in the following:
Because if-then statements whose reverse is correct are so common, many people mistakenly treat all if-
then statements as having correct reverses too, leading to incorrect deductions.
If a person has a contagious cold/²u, then the person will cough / If a person is coughing, then the
person has a contagious cold/²u. But the second true/false statement may be incorrect; the person
may have just eaten something that irritated the throat.
If a person is drunk, then the person will wobble when walking / If a person wobbles when walking,
then the person is drunk. But the second true/false statement may be incorrect; the person may have
a disability, as airline employees and others often ±nd out the hard way when seeing someone who
wobbles when walking or has slurred speech.
Screenshot source: Headline from above news article link, 2017.
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PARTICIPATION
ACTIVITY
4.5.2: If-then statements with and without correct reverses.
Indicate which everyday if-then statements are only correct forward (one-way) or whose
reverse is also correct (both ways).
1)
If Jo is Mia's child, then Mia is Jo's
parent.
One-way
Both ways
2)
If Pat is 16 now, then Pat was 15 a year
ago.
One-way
Both ways
3)
If a person has trouble walking, then the
person is (at least momentarily)
disabled.
One-way
Both ways
4)
If a person has a contagious rash, then
the skin will show the rash.
One-way
Both ways
5)
If my spouse is upset with me, my
spouse won't speak during a car drive.
One-way
Both ways
A common if-then statement both-way assumption after a disaster.
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A particularly sad both-way assumption error is often heard after a natural disaster. After
a hurricane devastates a city, one might hear "Well, those people chose to live in a
hurricane zone." The same is heard for ±res, tornadoes, ²oods, and other disasters.
Many people believe this if-then statement to be correct: If people knowingly choose to
live in a very dangerous area, then those people are likely to experience devastation. But
after a disaster, many people apply that if-then statement in reverse: If people
experienced devastation, then those people knowingly chose to live in a dangerous area.
But, just because devastation occurs in an area doesn't mean the area was known to be
dangerous. Even the east coast of Florida, which gets hit by many hurricanes, isn't
necessarily a dangerous area; the vast majority of homes experience no problems.
That logic error is likely a way of avoiding the pain a person experiences when
empathizing with others' suffering. But sometimes feeling that pain is perhaps what's the
most appropriate and human thing to do.
Photo sources: (Left) nypost.com
, (Right) time.com
4.6 Logic: AND/OR
True/false statements with AND/OR
A true/false statement may combine two (or more) other true/false statements, connected by AND or OR.
The logical AND
function evaluates to true only if all
sub-statements are true.
The logical OR
function evaluates to true if any
sub-statement is true.
PARTICIPATION
ACTIVITY
4.6.1: AND and OR logic functions.
Animation content:
unde±ned
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PARTICIPATION
ACTIVITY
4.6.2: True/false statements involving AND/OR.
Below, A as well as B are true/false sub-statements.
1)
What is A AND B, when A is false and B
is true?
True
False
2)
What is A AND B, when A is true and B
is true?
True
False
3)
What is A OR B, when A is false and B is
true?
True
False
4)
What is A OR B, when A is true and B is
true?
True
False
5)
What is A OR B, when A is false and B is
false?
True
False
Animation captions:
1. A person being at least 36 inches tall is a true/false statement, as is being at least 4 years old.
The statements can be combined using AND, forming a new true/false statement.
2. A table can be used to show the truth value of the AND statement depending on the truth
values of the two sub-statements.
3. AND evaluates to true only when both sub-statements are true. If a person is 38 inches tall and
5 years old, both sub-statements are true, so the person can ride.
4. But if a person is only 32 inches tall, the ±rst sub-statement is false, so the person cannot ride
(no matter whether the second sub-statement is true).
5. An OR statement is true if only one or both sub-statements are true. If either a person is under
30 inches OR under 7 years, or both, a car seat is required.
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6)
For the example above, can a 40-inch-
tall 4-year-old ride?
Yes
No
7)
For the example above, is a car seat
required for a 60-inch-tall 6-year-old?
Yes
No
8)
AND can apply to more than two sub-
statements. To what does A AND B
AND C evaluate when A is true, B is true,
C is false?
True
False
9)
OR can apply to more than two sub-
statements. To what does A OR B OR C
evaluate when A is true, B is false, C is
false?
True
False
10)
As with arithmetic expressions like (4
+ 2) * 3, logic expressions can be
longer and involve parentheses. To
what does (A AND B) OR C evaluate
when A is true, B is true, C is false?
True
False
PARTICIPATION
ACTIVITY
4.6.3: AND/OR logic in everyday English.
In everyday English, the words AND or OR are sometimes omitted. People must use common
sense to recognize whether the English meaning is AND or OR.
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1)
Does the following use AND logic or
instead use OR logic?
To enroll in the ABC preschool, students
must: (1) Be 4 years old or older, (2)
Have up-to-date immunizations.
AND
OR
2)
Does the following use AND logic or
instead use OR logic?
These jobs qualify for a museum
discount: (1) Teacher, (2) First-
responder, (3) Daycare worker.
AND
OR
OR in everyday English is sometimes exclusive
In everyday English, sometimes OR is used as above. For a rated-R movie, children under
17 can enter if accompanied by a parent or guardian. A parent, guardian, or both, enables
a child to enter.
But sometimes, OR is used in an exclusive manner. A menu says that a meal comes with
salad or soup. The OR clearly means only salad or only soup, but not both. In logic, this
form of OR is called "exclusive OR".
Unfortunately, English uses the same word for both concepts (aargh!). The reader should
realize that the ±eld of logic, and this material, uses OR to refer to the "inclusive" form of
OR (the parent/guardian example above), and will say "exclusive OR" explicitly if using
that form.
Negating an AND or OR expression
Some simple math increases the power of logic. A common example is ±nding the negation
of an
expression involving AND and OR, where the new expression evaluates to the opposite of the original.
The rules for negating an AND/OR expression are known as De Morgan's Laws
.
De Morgan's Laws
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The negation of A AND B, or NOT(A AND B), is NOT(A) OR
NOT(B).
The negation of A OR B, or NOT(A OR B), is NOT(A) AND
NOT(B).
PARTICIPATION
ACTIVITY
4.6.4: Negating an AND or OR expression.
PARTICIPATION
ACTIVITY
4.6.5: Negating a logic expression with AND / OR.
Indicate if the negation was done correctly.
1)
NOT(A AND B)
= NOT(A) OR B
Correct
Incorrect
2)
NOT(A AND B)
= NOT(A) AND NOT(B)
Correct
Incorrect
Animation content:
unde±ned
Animation captions:
1. In English, negating a logical AND expression can be tricky. What is the negation of a rule
requiring a rider to have a wristband AND that the rider is at least 5 years old?
2. De Morgan's Law helps. NOT(A AND B) = NOT(A) OR NOT(B). Each term is negated, and the
AND changes to OR.
3. Negating the English statement yields: NOT(rider has wristband) OR NOT(rider at least 5 yrs).
4. Negating each sentence yields: Rider lacks wristband OR rider under 5 yrs. The rider cannot ride
if either is true.
5. Negating an expression with OR is similar. In that case, the OR becomes an AND.
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3)
NOT(A AND B)
= NOT(A) OR NOT(B)
Correct
Incorrect
4)
NOT(A OR B)
= NOT(A) OR NOT(B)
Correct
Incorrect
5) NOT(NOT(A))
= A
Correct
Incorrect
6)
NOT(NOT(A) AND B)
= NOT(NOT(A)) OR NOT(B)
= A OR NOT(B)
Correct
Incorrect
If-then statements with AND/OR logic
In an if-then statement, the ±rst statement is often composed of sub-statements connected by AND or OR.
PARTICIPATION
ACTIVITY
4.6.6: If-then statements with AND/OR.
PARTICIPATION
ACTIVITY
4.6.7: If-then statements involving AND or OR logic.
Animation content:
unde±ned
Animation captions:
1. The IF part of an if-then statement is commonly built from sub-statements connected by AND
or OR.
2. If either sub-statement in the IF part is true, then "Must use car seat" is true.
3. Such if-then statements are commonly written differently in English, but can be converted to if-
then statement form.
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Below, A, B, C are each a true/false statement. Assume any given if-then statement is correct,
and only applies one way (as with any if-else statement unless otherwise noted or
understood).
1)
If A AND B, then C. What is C when A is
true and B is true?
True
False
Unknown
2)
If A AND B, then C. When A is true and B
is false, what is C?
True
False
Unknown
3)
If A OR B, then C. When A is true and B
is false, what is C?
True
False
Unknown
4)
If a dog is scared or angry, the dog will
bark.
Fact: The dog is angry.
Will the dog bark?
Yes
No
Unknown
5)
People must be at least 18 and in good
health to enter.
Fact: Joe is 20. Joe is in good health.
Can Joe enter?
Yes
No
Unknown
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6)
If a dog is scared or angry, the dog will
bark.
Fact: The dog is not scared. The dog is
not angry.
Will the dog bark?
Yes
No
Unknown
CHALLENGE
ACTIVITY
4.6.1: Logic: AND/OR/NOT.
525966.2980244.qx3zqy7
Start
2
3
4
5
Given: A is true, B is true.
A AND B is
A OR B is
Check
Next
4.7 AND/OR/NOT logic examples
Example: Web searches
Web searches on google.com and other web search engines involve AND and OR logic. The words in a
search by default are treated as being joined by AND. Ex: A search for "²u cold" is interpreted as "²u AND
cold", meaning found pages should discuss both ²us and colds. In fact, a person can type that AND
between words without changing the meaning of the search.
In contrast, typing "²u OR cold" means found pages should discuss either ²us or colds (perhaps both).
Search tools consider other factors when returning search results, but search strongly favors pages that
satisfy AND/OR logic.
1
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Figure 4.7.1: A search for ²u cold yields pages that each discuss both, but a
search for ²u OR cold yields 5 pages where 2 discuss only the ²u.
The same logic is used for email searches, photo searches, and more. A photo search for "cats dogs" will
favor photos having both a cat AND a dog in the photo, while "cats OR dogs" will favor photos having either
a cat, or a dog, or both.
Figure 4.7.2: Left: A search for cat dog in this person's photos yields no
results. Right: A search for cat OR dog yields numerous results, of just
dogs. Clearly this person is a dog-lover, and apparently doesn't have much
interest in cats.
Image source: Google search results screenshots, 2019.
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PARTICIPATION
ACTIVITY
4.7.1: Web searching and AND/OR logic.
What pages will be favored for the given search?
1)
Julia AND Roberts
Pages about Julia Roberts
Pages with the words Julia, AND,
and Roberts
Pages with either the word Julia,
the word Roberts, or both
2)
New York
Pages about New York
Pages about New, or about York,
or about both.
3)
Bees OR wasps
Pages that include discussion of
both bees and wasps on the
same page.
Pages that discuss bees only, or
that discuss wasps only, or that
discuss both.
Pages that contain the words
bees, OR, and wasps on the
same page.
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PARTICIPATION
ACTIVITY
4.7.2: Logic with AND and OR.
On a jet with two bathrooms, when bathroom 1 is occupied AND bathroom 2 is occupied, an
"all-bathrooms-are-occupied" red light turns on. In other words: IF bathroom 1 is occupied
AND bathroom 2 is occupied, THEN the red light turns on. The if-then statement's reverse is
also correct: IF the red light is on, THEN bathroom 1 is occupied AND bathroom 2 is occupied.
1)
Fact: Bathroom 1 is occupied.
Bathroom 2 is occupied.
Light is off
Light is on
2)
Bathroom 1 is occupied, but Bathroom
2 is not occupied.
Light is off
Light is on
3)
The light is red.
Both bathrooms are occupied
At least one bathroom is
unoccupied
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4)
Some signs don't just turn from on to
off when a bathroom is available, but
instead turn the light green. A person
sees the following bathroom-occupied
sign lit green.
Both bathrooms are unoccupied
At least one bathroom is
unoccupied
Example: Jaywalking laws
Laws make extensive use of AND/OR logic. For example, California law de±nes jaywalking as a person
crossing a street outside a crosswalk where the intersection to the left is controlled by a signal AND the
intersection to the right is controlled by a signal. (A signal is a tra´c light, meaning those red, yellow, and
green lights people see regularly). The law appears here
.
PARTICIPATION
ACTIVITY
4.7.3: California jaywalking law involves AND logic.
Laws are usually if-then statements whose reverse is also correct. If speci±c things are done, then a person
broke that law. AND, if the person broke that law, then the person did those speci±c things. In other words,
the ONLY way to jaywalk is to cross AND the left intersection is a signal AND the right intersection is a
signal.
PARTICIPATION
ACTIVITY
4.7.4: Jaywalking in California.
Animation content:
unde±ned
Animation captions:
1. CVC 21955: Between adjacent [signal-controlled] intersections, pedestrians shall not cross the
roadway [unless in a crosswalk].
2. As an IF-THEN statement: IF a person crosses AND left intersection is signal AND right
intersection is signal, THEN jaywalking has occurred.
3. If the left has a signal but the right has a stop sign, jaywalking did not occur. All three sub-
statements must be true: Crossed AND left is signal AND right is signal.
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Indicate whether jaywalking has occurred if a person crosses the street (outside a crosswalk),
between left and right intersections as noted.
1)
Left: Signal
Right: Signal
Yes
No
2)
Left: Stop sign
Right: Signal
Yes
No
3)
Left: Stop sign
Right: Stop sign
Yes
No
4)
The jaywalking law is an if-then
statement whose reverse is also
correct. A person is guilty of jaywalking.
Can one deduce that the person
crossed AND left was signal AND right
was signal?
Yes
No
5)
The actual law just says "controlled"
rather than "signal-controlled", and
de±nes an intersection as controlled if
the intersection has a signal OR an
o´cer. Does this sentence describe the
law's logic?
Jaywalking occurs if: A person crosses
outside a crosswalk AND (left is signal
OR o´cer) AND (right is signal OR
o´cer)
Yes
No
True story: Jaywalking ticket
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Tim was a student at a University of California college campus. He was walking home
from studying and safely crossed a street without any cars in sight, at a location between
a stop sign and a signal. He was stopped by a campus police o³cer who gave him a
jaywalking ticket. The o³cer believed the law meant that either intersection could be a
signal. Tim read the jaywalking law, and argued to a judge in court that the o³cer
misunderstood the logic and in fact both intersections had to be signals. Tim's ticket was
overturned by the judge.
Example: Car seat usage
The California law for car seat usage appears below. The law involves a lot of AND and OR logic.
Figure 4.7.3: California car seat law (2019).
Children under 2 years of age shall ride in a rear-facing car seat unless the child weighs
40 or more pounds OR is 40 or more inches tall.
Children under the age of 8 must be secured in a car seat or booster seat in the back
seat.
Children who are 8 years of age OR have reached 4'9" in height may be secured by a
booster seat, but at a minimum must be secured by a safety belt.
Below are the same rules, rewritten using if-then statements.
Figure 4.7.4: California car seat law written as if-then statements.
IF (child age is under 2 years) AND NOT( (child weight is 40+ pounds) OR (child height is
40+ inches) ), THEN must ride in rear-facing car seat.
IF (child age is under 8 years), THEN must ride in back seat in ( car-seat OR booster-seat
).
IF ( (child age is 8+ years) OR (child height is 4'9"+), THEN must use (booster-seat OR
safety-belt).
PARTICIPATION
ACTIVITY
4.7.5: Car seat law.
Consider the car seat law above.
Source: California Highway Patrol
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1)
May a 1.5 year old child weighing 30
pounds and with height 30 inches ride
in a forward-facing car seat?
Yes
No
2)
May a 5 year old weighing 70 pounds
ride in the front seat?
Yes
No
3)
May a 9 year old weighing 38 pounds
use just a seat belt?
Yes
No
4.8 Common applications of logic
Laws
Laws make extensive use of if-then logic (usually both-way: the reverse is also correct)), including AND/OR
logic. In everyday life, people need to understand laws to avoid breaking laws. Plus, many people may serve
on a jury someday, where judges ask jury members to evaluate the logic of a law carefully. Juries only
decide what are the facts of a case, namely which facts are true or false. Given those facts, juries should
apply the law's logic, whether a juror agrees with the logic or not.
Figure 4.8.1: Laws on calling police after an accident.
Many people don't realize that most states have a law that requires
a person to contact the
police after a car accident, sometimes immediately, sometimes within a few days. Below are a
few such laws from various states, taken from AAA.com (2019). Many such laws make use of
OR logic: IF injury OR death OR damage exceeds some amount, THEN police must be noti±ed.
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Arizona: Crashes are required to be reported when property damage exceeds
$300.00, results in bodily injury to or death of a person, or if the settlement of the
crash has not been reached within 6 months of the crash.
California: Crashes are required to be reported in cases of death or injury or when
property damage exceeds $1,000. Reports must be ±led within 10 days.
Florida: Crashes are required to be reported as soon as possible in cases of death or
injury, or when property damage exceeds $500.00.
Nevada: Crashes are required to be immediately reported.
Washington: Crashes are required to be reported in cases of death, injury, or when
property damage exceeds $700.00. The deadline to ±le a report is 4 days.
PARTICIPATION
ACTIVITY
4.8.1: Contacting police after an accident.
Jay was involved in a car accident yesterday. Damage is about $500, no injuries, no deaths.
According to the laws listed above, is Jay required to contact the police in the given state?
Note: Even if not required, many people recommend calling the police anyways to have them
come to the accident scene and ±le a report.
1) California
Yes
No
2) Arizona
Yes
No
3) Nevada
Yes
No
Ouch. Frank's daughter was in another accident. Everyone was OK. Phew. This time the truck survived too.
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Figure 4.8.2: Laws on leaving animals in cars.
A car's inside can heat up quickly when parked in the sun. 80°F outside can turn into well over
100°F inside. Thus, many states now have laws against endangering animals in parked cars.
Furthermore, many states have laws granting immunity to people who break into a car to save
an animal in danger. Below are those two laws in California Penal Code 597.7
:
A person shall not leave or con±ne an animal in any unattended motor vehicle under
conditions that endanger the health or well-being of an animal due to heat, cold, lack of
adequate ventilation, or lack of food or water, or other circumstances that could
reasonably be expected to cause suffering, disability, or death to the animal.
A person who removes an animal from a vehicle [believing the animal to be in immediate
danger] is not criminally liable ... if the person does all of the following:
(A) Determines the vehicle is locked or there is otherwise no reasonable manner
for the animal to be removed from the vehicle.
(B) Has a good faith belief that forcible entry into the vehicle is necessary because
the animal is in imminent danger of suffering harm if it is not immediately removed
from the vehicle, and, based upon the circumstances known to the person at the
time, the belief is a reasonable one.
(C) Has contacted a local law enforcement agency, the ±re department, animal
control, or the "911" emergency service prior to forcibly entering the vehicle.
(D) Remains with the animal in a safe location, out of the elements but reasonably
close to the vehicle, until a peace o´cer, humane o´cer, animal control o´cer, or
another emergency responder arrives.
(E) Used no more force to enter the vehicle and remove the animal from the vehicle
than was necessary under the circumstances.
(F) Immediately turns the animal over to a representative from law enforcement,
animal control, or another emergency responder who responds to the scene.
PARTICIPATION
ACTIVITY
4.8.2: Rescuing animals from hot vehicles.
Consider the California laws above regarding leaving animals in a car.
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1)
Kim rescues a dog from a car in 102°F
weather by breaking a window, but did
not check if the car was unlocked ±rst.
Does the law grant Kim immunity?
Yes
No
2)
Riley sees a cat in a car in 102°F
weather, and the cat appears to be
severely dehydrated. Riley ±nds that
every door is locked and no windows
are open. Riley breaks a window to
rescue the cat, then gives the cat water,
then calls 911, then waits in an air-
conditioned car, and then turns the cat
over to arriving police. Does the law
grant Riley immunity?
Yes
No
Soccer rules
Soccer is a popular sport among kids worldwide and increasingly in the U.S. too. Many parents must learn
the rules (called laws) to serve as coaches or referees, or just to better enjoy the game. Below are a few
common soccer laws.
Table 4.8.1: Common soccer laws.
Law
Written emphasizing the logic
At the moment of delivering the ball, the
thrower must:
stand facing the ±eld of play
have part of each foot on the
touchline or on the ground outside
the touchline
throw the ball with both hands
from behind and over the head
from the point where it left the
±eld of play.
At moment of delivering ball, IF
face-±eld AND
(feet on touchline OR feet on ground
outside touchline) AND
((behind head AND over head) AND where
it left ±eld)
THEN throw-in is legal.
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A player is cautioned [yellow card] if
guilty of:
delaying the restart of play
dissent by word or action
entering, re-entering or deliberately
leaving the ±eld of play without the
referee's permission
failing to respect the required
distance when play is restarted
with a corner kick, free kick or
throw-in
persistent offences (no speci±c
number or pattern of offences
constitutes 'persistent')
IF a player
delays restart OR
(dissents by word OR dissents by action)
OR
((enters OR re-enters OR leaves) AND
NOT(had permission)) OR
((corner kick OR free kick OR throw in)
AND fails to respect distance) OR
commits persistent offences
THEN the player is cautioned [yellow card]
(Originally-worded law for penalty kick
omitted here; appears in IF-THEN form
to the right).
IF
(Ball stationary AND ball on penalty mark)
AND
Kicker identi±ed AND
Goalkeeper is (on goalline AND facing
kicker AND between posts AND
NOT(touching post OR touching bar OR
touching net)) AND
Other players are (at least 10 yards away
AND behind penalty mark AND on ±eld
AND outside penalty area)
THEN ready for penalty kick.
PARTICIPATION
ACTIVITY
4.8.3: Logic and soccer rules.
1)
A soccer player is getting ready to throw
the ball back onto the ±eld. The player
jumps in the air and throws the ball
from behind and over the player's head.
Is this play allowed?
Yes
No
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2)
A player abruptly leaves the ±eld
without informing the referee, but does
not delay the restart of play. Should the
referee give the player a yellow card?
Yes
No
3)
The teams are preparing for a penalty
kick. This situation means the
requirement for the ball to be stationary
and on the penalty mark must be met.
Yes
No
4.9 Logical induction
Logical induction
Logical deduction yields a certain result. Given a correct if-then statement like "If Fido is scared, then Fido
will bark", when data/facts indicate "Fido is scared" is true, then for certain "Fido will bark" will be true too.
In contrast, logical induction
is a kind of logic that is uncertain: Given that several true/false statements are
true, a person generalizes that another statement is true. Ex: If a person sees a baby that cries a lot, then
another baby that cries a lot, then a third baby that cries a lot, the person may generalize: Babies cry a lot.
PARTICIPATION
ACTIVITY
4.9.1: Logical deduction is certain, while logical induction is an informed guess.
Animation content:
unde±ned
Animation captions:
1. In logical deduction, given if-then statements, one true/false statement's truth value can be
used to deduce another statement's truth value. If F is true, then A is true.
2. If A is true, then B is true. So if F is true, then B certainly must be true.
3. Another form of logic is induction, which generalizes. Mia loves puppies. Jan loves puppies.
Generalizing: "People love puppies".
4. Induction is an informed guess. Perhaps all people really do love puppies. Or perhaps some
people don't. While not certain, induction is common and useful.
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PARTICIPATION
ACTIVITY
4.9.2: Logical induction.
Given the true/false statements are true (facts), select the best logical induction.
1)
Val likes apples. Cindy likes apples. Stu
likes apples.
People like apples
People don't like oranges
2)
Lee likes apples. Lee like oranges. Lee
likes grapes. Lee likes melon.
Lee likes apples, oranges, grapes,
and melon
Lee likes fruit
3)
A gallon of milk is heavy. A gallon of
orange juice is heavy. A gallon of apple
juice is heavy. A gallon of cereal is light.
A gallon of anything is heavy
A gallon of liquid is heavy
4)
Fido heard sirens 10 times today and
barked 9 of those times.
Fido barks when hearing sirens
Nothing should be induced
PARTICIPATION
ACTIVITY
4.9.3: Logical induction vs. deduction.
Indicate whether the logic is induction or deduction.
1)
Given: If A, then B.
Fact: A is true.
So B must be true.
Induction
Deduction
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2)
Hotel XYZ's rate was high 2 months
ago.
Hotel XYZ's rate was high last month.
Hotel XYZ's rate is high this month.
So hotel XYZ is expensive.
Induction
Deduction
Common induction mistakes
Induction is a widely used form of logic. In fact, generalizing is largely how humans learn and is essential to
human survival. Ex: A child pulls a dog's tail, and the dog angrily snaps, scaring the child. The child
generalizes that pulling a dog's tail is dangerous.
While essential to survival, logical induction is often wrong. Humans may wish to be aware that many of
their beliefs are statements thought to be true, but in fact not always true or just plain false, due to incorrect
logical induction. Some logical induction leading to incorrect beliefs about humans is called stereotyping
.
PARTICIPATION
ACTIVITY
4.9.4: Logical induction is important, but is sometimes wrong.
Indicate whether the proposition obtained via logical induction is likely to be true.
1)
A manager hired two students from
University of Spring±eld who turned out
to be great workers. The manager
decides: Students from University of
Spring±eld are great.
Likely
Unclear
2)
A manager hired 50 students from
University of Spring±eld and 50 from
University of Shelbyville. 45 of the
Spring±eld students had to be ±red,
while 48 of the Shelbyville students
worked out great. The manager
decides: Students from University of
Shelbyville are better than students
from University of Spring±eld.
Likely
Unclear
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3)
Jay has met a few homeschooling
families and ±nds the kids socially
awkward. Jay concludes:
Homeschooling causes social
awkwardness.
Likely
Unclear
4)
Flo notices that one particular dog
breed seems to show up a lot in "lost
dog" ²yers. Flo concludes: Dogs of that
breed are more likely to get loose.
Likely
Unclear
5)
The U.S. Surgeon General states:
Smoking kills. In other words: If a
person smokes, a person is more likely
to die earlier than otherwise. Stan says,
"I don't believe that. My Grandpa
smoked his whole life and lived to be
92." Stan induces: Grandpa smoked and
didn't die early, so smokers don't die
early. Is Stan's induction likely to be
true?
Yes
No
4.10 Sets and Venn diagrams
Venn diagrams
Logic operations like AND and OR are often performed on sets. A set
is a collection of items, like all people
who have student loans, or all people who have credit-card debt.
Performing an AND operation on two sets is called intersection
. Ex: The intersection of the set of
college students and the set of students above age 19 is the set of college students above age 19.
Performing an OR operation on two sets is called union
. Ex: The union of the set of college students
and the set of college employees is the set of college students, college employees, and college
student employees.
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A Venn diagram
depicts sets graphically, which can be especially helpful for showing intersection and
union.
PARTICIPATION
ACTIVITY
4.10.1: Venn diagrams.
PARTICIPATION
ACTIVITY
4.10.2: Venn diagram of people with student loans and with credit card debt.
Consider the Venn diagram at the bottom left of the animation above.
1)
The XYZ organization wants to help
people get out of debt. The organization
wants to focus on people who have
both student loans and credit card debt,
as such people may be in the most
trouble. Looking at the Venn diagram
above, who should XYZ reach out to?
Jo, Kyle
Mia, Jo, Kyle, Lee, Sam
2)
The ABC organization wants to help
everyone who has any kind of student
loan or credit card debt. Looking at the
Venn diagram above, who should ABC
reach out to?
Mia, Lee, Sam
Mia, Jo, Kyle, Lee, Sam
Animation content:
unde±ned
Animation captions:
1. A set is a collection of items, such as people with student loans. Ex: Jo, Kyle, and Mia have
student loans and thus form a set.
2. Another set is people with credit card debt. Ex: Sam, Lee, Kyle, and Jo all have credit card debt.
3. In a Venn diagram, people with loans may be in a blue circle and people with credit card debt in
an orange circle. Each person is shown only once, so the circles overlap.
4. The people who have student loans AND credit card debt (intersection) are the people in the
overlapping region of the two circles, in this case Jo and Kyle.
5. The people who have student loans OR credit card debt (union) are the people in either or both
circles, so Mia, Jo, Kyle, Lee, and Sam.
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3)
An organization has the following rule:
IF a person has a student loan AND a
person has credit card debt, THEN the
person quali±es for assistance. In the
Venn diagram above, who quali±es?
Jo, Kyle
Mia, Jo, Kyle, Lee, Sam
PARTICIPATION
ACTIVITY
4.10.3: Sets and Venn diagrams.
Consider the Venn diagram below showing the set of people who have worked over 20 years,
and the set of people aged over 50 years, at a particular company.
1)
Who is everyone that has worked over
20 years?
Mike, Kee
Mike, Kee, Stu
Mike, Kee, Stu, Flo, Vu, Sal
2)
Who is everyone that is aged over 50
years?
Mike, Kee, Stu, Flo, Vu, Sal
Flo, Vu, Sal
Stu, Flo, Vu, Sal
3)
Who is everyone that has worked over
20 years and is aged over 50 years?
Stu
Mike, Kee, Stu, Flo, Vu, Sal
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4)
The company boss wants to offer an
early-retirement package to everyone at
the company who is aged over 50 years
and has worked over 20 years. Which
set operation is appropriate?
Union
Intersection
5)
The company boss wants to give a gift
to anyone who has worked over 20
years or is aged over 50 years. Which
set operation is appropriate?
Union
Intersection
6)
The company boss makes a rule: IF a
person has worked over 20 years OR a
person is aged over 50 years, THEN the
person should get a gift. Who should
get a gift?
Mike, Kee, Flo, Vu, Sal
Mike, Kee, Stu, Flo, Vu, Sal
7)
The company boss wants to know who
has worked over 20 years but is not
aged over 50 years. Who are those
people?
Mike, Kee
Mike, Kee, Stu
Flo, Vu, Sal
Example: Cold and ±u Venn diagrams
The Venn diagram below was published by a government health agency. The diagram quickly helps
determine whether a person's symptoms suggest a cold or ²u (in²uenza). Notice how much more
understandable the diagram is versus similar descriptions in textual or tabular form.
Figure 4.10.1: Venn diagram of cold and ²u symptoms.
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PARTICIPATION
ACTIVITY
4.10.4: Venn diagram for healthy behaviors.
Consider the Venn diagram above.
1)
How many sets are shown?
1
2
2)
In the sets labeled Cold and In²uenza,
what are the members of each set?
The people who have that illness
The symptoms of each illness
3)
Runny nose is a symptom of which
illness?
Cold only
In²uenza only
Both cold and in²uenza
4)
Sore throat is a symptom of which
illness?
Cold only
In²uenza only
Both cold and in²uenza
Depicting overlapping sets
Source: Dept. of Health and Human Services, Montana
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Venn diagrams are commonly used to depict overlapping sets of items without actually showing the set
members.
PARTICIPATION
ACTIVITY
4.10.5: Venn diagrams commonly show sets without showing members.
PARTICIPATION
ACTIVITY
4.10.6: Venn diagram for sets without showing members.
Consider the Venn diagrams above.
1)
Considering the Venn diagram on the
left, how many applicants have the
required technical skills and good social
skills?
About 15
About 15%
Unknown
2)
Considering the Venn diagram on the
right, does a region exist for people who
have technical skills and experience, but
lack social skills?
Yes
No
3)
How many initial sets are shown on the
right?
1
2
3
Animation content:
unde±ned
Animation captions:
1. Venn diagrams can just depict sets without showing members. Here, a hiring manager depicts
that some applicants have technical skills and others have social skills.
2. The manager wants people to understand that the ideal hires are people who are members of
both sets. The Venn diagram helps people understand the manager's point.
3. Venn diagrams are commonly used for more than two sets. Here, the manager adds a third set:
People having experience. The ideal hire is a member of all three sets.
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Venn diagrams for humor
Venn diagrams are sometimes used to make a point in a humorous way. Below is a
commonly-shared Venn diagram related to social media posting.
Venn diagrams with data
Sometimes a Venn diagram is annotated with data to indicate how many items fall into each region. The
±gure below is from an article summarizing people who follow common healthy-living recommendations,
namely: avoiding smoking, eating fruits and vegetables, and doing physical activity.
Figure 4.10.2: Venn diagram of healthy behaviors in Americans.
Source: CDC
The reader is encouraged to notice how elegantly the Venn diagram depicts the three sets of people, and
how easily various questions about the groups can be answered, such as "What percentage of people eat
fruits/vegetables but also smoke and don't do physical activity?" The answer is easily seen to be 2%: The
portion of the left circle that is outside the other two circles.
PARTICIPATION
ACTIVITY
4.10.7: Venn diagram for healthy behaviors.
Consider the Venn diagram above.
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1)
What percentage of people abstain
from smoking?
47%
76%
100%
2)
What percentage of people do all three
healthy behaviors: abstain from
smoking, eat fruits/vegetables, and do
physical activity?
5%
14%
100%
3)
What percentage of people eat
fruits/vegetables and do physical
activity, but smoke?
1%
6%
No such people exist
4)
What percentage of people do at least
one of the three healthy behaviors?
83%
100%
118%
5)
What percentage of people don't do any
of the three healthy behaviors?
1%
18%
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