logic THE SCIENCE OF REASONING People use
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logic THE SCIENCE OF REASONING People use reasoning all the time, some good some bad. Good or bad is NOT a matter of opinion. Logic can be challengingeven for very smart people. It takes hard work and patience to think well. Learning logic
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01
logic THE SCIENCE OF REASONING<br>
02
People use reasoning all the time, some good some bad.
Good or bad is NOT a matter of opinion.
Logic can be challenging—even for very smart people.
It takes hard work and patience to think well.<br>
Good or bad is NOT a matter of opinion.
Logic can be challenging—even for very smart people.
It takes hard work and patience to think well.<br>
03
Learning logic is like taking your brain to the gym<br>
04
Here some bad:
Some women are baseball fans. And some mothers are baseball fans. Thus, all women are mothers.
An earthquake occurred in San Francisco after the senator’s speech. Thus, that senator’s speech caused the earthquake.
Here some good:
All bears are mammals. Grizzlies are bears. Thus, grizzlies are mammals.
All U.S. Presidents are politicians. Thus, the current U.S. Presidents is a politician.
What makes the first list of reasoning bad and the second good? That’s what logic studies.<br>
Some women are baseball fans. And some mothers are baseball fans. Thus, all women are mothers.
An earthquake occurred in San Francisco after the senator’s speech. Thus, that senator’s speech caused the earthquake.
Here some good:
All bears are mammals. Grizzlies are bears. Thus, grizzlies are mammals.
All U.S. Presidents are politicians. Thus, the current U.S. Presidents is a politician.
What makes the first list of reasoning bad and the second good? That’s what logic studies.<br>
05
Let’s start with analytic vs. synthetic and a priori vs. a posteriori<br>
06
Any sentence has a Subject and a Predicate.
“Tomatoes are red”
Tomatoes = Subject
Red = Predicate<br>
“Tomatoes are red”
Tomatoes = Subject
Red = Predicate<br>
07
DEFINITION: A statement is Analytic if, and only if, the predicate concept is contained in the subject concept.
“All bachelors are unmarried men”
Subject: Bachelors
Predicate: Unmarried men
The concept of being an unmarried man defines what it is to be a bachelor.<br>
“All bachelors are unmarried men”
Subject: Bachelors
Predicate: Unmarried men
The concept of being an unmarried man defines what it is to be a bachelor.<br>
08
DEFINITION: A statement is Synthetic if, and only if, the predicate concept is NOT contained in the subject concept.
“All bachelors are tall”
Subject: Bachelors
Predicate: Tall
The predicate concept does not define the subject concept<br>
“All bachelors are tall”
Subject: Bachelors
Predicate: Tall
The predicate concept does not define the subject concept<br>
09
All objects occupy space The Sun is 93 million miles from earth’ Analytic Synthetic A bachelorette is a young unmarried woman Analytic<br>
10
a priori vs. a posteriori<br>
11
DEFINITION: A Priori means that something can be known independently of experience
By “experience” I mean sensory experience—see, touch, hear, taste, smell.
Can you think of an example of something you know to be true although you have not seen it or heard it or touched it or smelled it? “My friend Famuda is a bachelor.”
How do you know that he is a man?
True in all possible worlds(?)<br>
By “experience” I mean sensory experience—see, touch, hear, taste, smell.
Can you think of an example of something you know to be true although you have not seen it or heard it or touched it or smelled it? “My friend Famuda is a bachelor.”
How do you know that he is a man?
True in all possible worlds(?)<br>
12
DEFINITION: A Posteriori means that to know whether something is true you need to verify it through experience.
My friend Mark likes pizza.
How do you know that he likes pizza?<br>
My friend Mark likes pizza.
How do you know that he likes pizza?<br>
13
Analytic or synthetic?How do you know?<br>
14
Fire burns your fingers Fire definition = Combustion or burning, in which substance combine chemically with oxygen.<br>
15
The shortest distance between two points is a straight line Straight line definition = line traced by a point traveling in a constant direction; a line of zero curvature<br>
16
that rat is a rodent Rat definition = a rodent<br>
17
Graham's number is bigger than the number of atoms in the observable Universe, which is estimated to be 1082. There are prime numbers larger than Graham’s number.<br>
18
Snow is white Snow definition = atmospheric water vapor frozen into ice crystals and falling in light white flakes or lying on the ground as a white layer.
White definition: the lightest color and is achromatic (having no hue)<br>
White definition: the lightest color and is achromatic (having no hue)<br>
19
Ice is frozen water<br>
20
Children play with toys<br>
21
Planet earth rotates on its axis<br>
22
All objects have weight<br>
23
When a stone violently hits a glass window the glass breaks<br>
24
If An object is red, then that object is colored<br>
25
If you release a cellphone in air, the cellphone will fall downward<br>
26
Water drowns<br>
27
Great Job! Now, let’s discuss arguments<br>
28
Every science has a Subject matter Biology = living organisms
Mathematics = numbers.
Logic = arguments.
In logic, an argument is a piece of reasoning used to show or express or prove a point.<br>
Mathematics = numbers.
Logic = arguments.
In logic, an argument is a piece of reasoning used to show or express or prove a point.<br>
29
ARGUMENT DEFINITION A group of statements called “premises” given in support of a conclusion.
Conclusion is the main point or thesis.
A paper, a speech, a book, an article, an oral presentation, can be arguments.<br>
Conclusion is the main point or thesis.
A paper, a speech, a book, an article, an oral presentation, can be arguments.<br>
30
RECOGNIZE ARGUMENTS<br>
31
Every literature major must take a course in Shakespeare. John has taken the Shakespeare course; therefore, he must be a literature major.<br>
32
A time-honored policemen adage has it that with homicide, if you haven’t nailed your killer inside a week, your chances of ever doing so divide by half for every subsequent week that passes.<br>
33
If the president dies in office, then the first lady becomes the new president. Since the president has died in office, then his wife becomes the president.<br>
34
A person can’t be a marine and a sailor both. Since Max is a sailor, it must be that Max is not a marine.<br>
35
There is freedom in the sense of being able to move as one pleases, freedom in the sense of being able to do and speak as one pleases, and freedom in the sense of being able to think for oneself. This last type makes the others possible. Consequently, it is our most important freedom.<br>
36
Every chemistry major must take a year of organic chemistry. Jose is a chemistry major, so Jose takes a year of organic chemistry.<br>
37
You shouldn’t buy a foreign car. Patrick did, and within a year he had to have the transmission replaced.<br>
38
Most people who major in the humanities go on to teach humanities. People who teach the humanities are happy because the humanities are always exciting and fun, and they are about things of human importance. Work that keeps you focused on being human is hardly work at all. It comes to be a labor of love. People who major in the humanities love their work.<br>
39
I heard that most MDs are conservatives. My doctor is an MD. So, my doctor is a conservative.<br>
40
When a mild electrical current is applied to a muscle, the muscle contracts. When the current stops, the muscle relaxes. Therefore, the application of a mild current to a muscle is the cause of contraction.<br>
41
Some fruits are sweet. Honey is sweet. Therefore, honey must be a fruit.<br>
42
Computers don’t have feelings because only living things can have feelings. And computers are not living things.<br>
43
Research has shown that people who do at least 30 minutes a day of vigorous exercise reduce their risk of heart disease and some forms of cancer. It would be wise for you to begin a daily program of exercise.<br>
44
All this talk about banning guns makes me sick! Isn't it obvious that if we ban guns, law-abiding citizens will not own them, while only the criminals will have them?<br>
45
Enthymemes An argument missing a premise, or a conclusion, is an enthymeme<br>
46
Enthymemes: Arguments with missing parts All chemists are scientists
So, Mark is a scientist. Mark is a chemist<br>
So, Mark is a scientist. Mark is a chemist<br>
47
All bridges in NYS were built by aliens.
Brooklyn is in NYS.
The Brooklyn Bridge is in Brooklyn. So, the Brooklyn Bridge was built by aliens<br>
Brooklyn is in NYS.
The Brooklyn Bridge is in Brooklyn. So, the Brooklyn Bridge was built by aliens<br>
48
Dude, Wendy’s is the best restaurant on the planet! They have the Jr. Bacon Cheeseburger there, and it tastes awesome. A restaurant that serves the Jr. Bacon Cheeseburger is the best on the planet<br>
49
Roger Maris' record of 61 homeruns in a single season stood from 1961 until 1998! He should be admitted into the Baseball Hall of Fame. Anyone with that record should be in the Baseball Hall of Fame.<br>
50
Two teenagers saw the movie, Natural Born Killers and went out on a killing spree. Several teenagers who have committed violence have spent many hours playing video games filled with murder and violence. We must have some stricter controls on the content of entertainment that is viewed by teenagers. Spending many hours playing video games filled with murder and violence causes teenagers to commit violence.<br>
51
GOOD ARGUMENTS What’s A Good Argument?<br>
52
an argument IS good when, and only when True premises.
And a conclusion that follows from the premises.
A conclusion may follow either necessarily or probably.
FOLLOWS MEANS: given the premises, the conclusion is expected to be the case.
NECESSITY and PROBABILITY imply 2 different reasoning processes.<br>
And a conclusion that follows from the premises.
A conclusion may follow either necessarily or probably.
FOLLOWS MEANS: given the premises, the conclusion is expected to be the case.
NECESSITY and PROBABILITY imply 2 different reasoning processes.<br>
53
1. DEDUCTION 2. INDUCTION If the conclusion follows necessarily = DEDUCTIVE.
If the conclusion follows probably = INDUCTIVE.
If you are in Brooklyn (NY), you are in the US.
And you are in Brooklyn.
It follows that…<br>
If the conclusion follows probably = INDUCTIVE.
If you are in Brooklyn (NY), you are in the US.
And you are in Brooklyn.
It follows that…<br>
54
Necessity vs probability Philosophers and scientists recognize conditions among events or logical relationships. Conditions can be necessary and sufficient.<br>
55
Sufficient Conditions DEFINITION: “X is a sufficient condition for Y” means that if we have X, Y must be there. In other words, X guarantees Y. Or in other, other words, given X, Y must follow.<br>
56
Necessary Conditions DEFINITION: “X is a necessary condition for Y” means that if X is not there, then Y will not be there, either.
However, to say that X is a necessary condition for Y does not mean that X guarantees Y.
For instance, oxygen is necessary for a match to catch fire, but it doesn’t guarantee it. The match can be surrounded by oxygen, but still not catch fire. However, the match needs oxygen to catch fire.<br>
However, to say that X is a necessary condition for Y does not mean that X guarantees Y.
For instance, oxygen is necessary for a match to catch fire, but it doesn’t guarantee it. The match can be surrounded by oxygen, but still not catch fire. However, the match needs oxygen to catch fire.<br>
57
Partial Cause DEFINITION: A is a partial cause of B just if other factors make the occurrence of A increase the likelihood of B. But A is neither sufficient not necessary to cause B.
Rapidly falling atmospheric pressure is a partial cause to precipitation. But falling pressure is neither sufficient nor necessary.
Fog is the product of many factors occurring simultaneously: high pressure, warm air ascends, temperature fall, cooler air trapped near the ground, absence of wind, humidity increase = fog.<br>
Rapidly falling atmospheric pressure is a partial cause to precipitation. But falling pressure is neither sufficient nor necessary.
Fog is the product of many factors occurring simultaneously: high pressure, warm air ascends, temperature fall, cooler air trapped near the ground, absence of wind, humidity increase = fog.<br>
58
necessary Power failure causes the loss of data in a computer’s memory.
How does the effect (the loss of data) come about? If power failure occurs while you’re typing your essay, we know that loss of data will occur. We can say that power failure is a sufficient condition for the loss of data.
If there is power failure, there is loss of data.
But if there is loss of data, it is not necessary that there is power failure. Other causes might explain the loss of data. So, power failure is not a necessary condition for the loss of data; power failure is a sufficient condition.<br>
How does the effect (the loss of data) come about? If power failure occurs while you’re typing your essay, we know that loss of data will occur. We can say that power failure is a sufficient condition for the loss of data.
If there is power failure, there is loss of data.
But if there is loss of data, it is not necessary that there is power failure. Other causes might explain the loss of data. So, power failure is not a necessary condition for the loss of data; power failure is a sufficient condition.<br>
59
NECESSARY The presence of oxygen caused the combustion in an engine.
The presence of oxygen causes combustion. Is it the only cause? No. you need others, gasoline, a battery, etc.
So, we say that oxygen is a necessary condition—necessary but not sufficient.<br>
The presence of oxygen causes combustion. Is it the only cause? No. you need others, gasoline, a battery, etc.
So, we say that oxygen is a necessary condition—necessary but not sufficient.<br>
60
both necessary and sufficient “Sam's being a father is a condition both necessary and sufficient for Sam’s being a male parent.
Your presence in class is a condition both sufficient and necessary for my marking you as “present.”
Your arriving first at a marathon is a condition both sufficient and necessary for you to be the winner.<br>
Your presence in class is a condition both sufficient and necessary for my marking you as “present.”
Your arriving first at a marathon is a condition both sufficient and necessary for you to be the winner.<br>
61
CONTRIBUTING factors Smoking causes cancer.
How does smoking cause cancer? We know that smoking is not sufficient to get cancer, since many people smoke but never get cancer.
Is smoking necessary to get cancer? No. you may get cancer for other reasons.
Thus, we call smoking a contributing factor or partial cause of cancer.<br>
How does smoking cause cancer? We know that smoking is not sufficient to get cancer, since many people smoke but never get cancer.
Is smoking necessary to get cancer? No. you may get cancer for other reasons.
Thus, we call smoking a contributing factor or partial cause of cancer.<br>
62
More examples Having gasoline in my car is a necessary condition for my car to start. Without gasoline my car will not start. But having gasoline in the car does not guarantee that my car will start. There are many other conditions needed for my car to start. Gasoline is necessary, but not sufficient.<br>
63
Having oxygen in the earth’s atmosphere is a necessary condition for human life. But it will not guarantee human life. There are many other conditions needed for human life other than oxygen. Oxygen is necessary, but not sufficient.<br>
64
Being 35 years of age is a necessary condition for becoming the president of the US. Being 35 does not guarantee that a person will become the president of the US. There are many other conditions that lead to a person becoming the president of the US than being 35 years of age. Again, necessary, but not sufficient.<br>
65
Earning a total average of 98 in this class is a sufficient condition for earning a final grade of A. Your averaging 98 guarantees that you will receive an A.
But it is not necessary to earn an average of 98 to earn an A. You can earn an average of 94, 94.5, 95, 95.5…100 to earn an A.
Earning a final grade of C is a sufficient condition for passing the course. But it’s not necessary. You can pass with a B or C+ or A-.
Rain pouring from the sky is a sufficient condition for the ground to be wet. But it is not necessary for rain to be pouring from the sky for the ground to be wet. The sprinkler could take care of that as well.<br>
But it is not necessary to earn an average of 98 to earn an A. You can earn an average of 94, 94.5, 95, 95.5…100 to earn an A.
Earning a final grade of C is a sufficient condition for passing the course. But it’s not necessary. You can pass with a B or C+ or A-.
Rain pouring from the sky is a sufficient condition for the ground to be wet. But it is not necessary for rain to be pouring from the sky for the ground to be wet. The sprinkler could take care of that as well.<br>
66
Events involve many circumstances. For example, a woman falls in a store and breaks a hip. There are many factors: The wet floor, the custodian forgot to put the WET FLOOR sign, the texture of the floor, the woman’s high heel shoes that she might not have if her other shoes were repaired, in which case she would not have fallen, her age, the fact that she lingered around to talk to the clerk…
All these factors converging at different places have a bearing on the complex event. WHAT CAUSES WHAT<br>
All these factors converging at different places have a bearing on the complex event. WHAT CAUSES WHAT<br>
67
We distinguish causal factor by proximity to the effect.
A proximate cause is a causal factor that occurs immediately prior to the cause. The impact with the hard floor is the proximate cause of the hip fracture.
The lack of WET FLOOR sign is the immediate cause. Immediate cause is a causal factor whose presence contribute to the effect but not directly.
The woman’s shoes not being repaired is the remote cause. Remote cause is a contributing cause, but it is removed from the event.<br>
A proximate cause is a causal factor that occurs immediately prior to the cause. The impact with the hard floor is the proximate cause of the hip fracture.
The lack of WET FLOOR sign is the immediate cause. Immediate cause is a causal factor whose presence contribute to the effect but not directly.
The woman’s shoes not being repaired is the remote cause. Remote cause is a contributing cause, but it is removed from the event.<br>
68
Deductive logic<br>
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DEDUCTION is a process of reasoning from premises to a necessary conclusion.
Given the premises, if the conclusion does follow necessarily, a deductive argument is called is VALID.
Given the premises, if the conclusion does not follow at all, a deductive argument is called INVALID.<br>
Given the premises, if the conclusion does follow necessarily, a deductive argument is called is VALID.
Given the premises, if the conclusion does not follow at all, a deductive argument is called INVALID.<br>
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valid All books are objects.
This is a book.
This is an object.<br>
This is a book.
This is an object.<br>
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invalid All books are objects.
This is an object.
This is a book.<br>
This is an object.
This is a book.<br>
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VALID despite false premises If you live in Brooklyn (NY), you are in South America.
You live in Brooklyn.
Therefore, you are in South America.
This argument is UNSOUND.<br>
You live in Brooklyn.
Therefore, you are in South America.
This argument is UNSOUND.<br>
73
Valid with TRUE PREMISES is sound All physical objects occupy space.
My book is a physical object.
Therefore, my book occupies space.<br>
My book is a physical object.
Therefore, my book occupies space.<br>
74
Valid or invalid? If you play soccer, you have a ball.
Your have a ball.
You play soccer.<br>
Your have a ball.
You play soccer.<br>
75
invalid despite all true premises Oxygen is required for human life.
Earth’s atmosphere contains oxygen.
Therefore, there is human life on earth.<br>
Earth’s atmosphere contains oxygen.
Therefore, there is human life on earth.<br>
76
RECOGNIZE VALID ARGUMENTS<br>
77
It is important to recognize valid arguments because if an argument is valid, it can be a good argument, a sound argument.
Certain forms are always valid. So regardless of the content, if an argument has a certain form, it is automatically valid.<br>
Certain forms are always valid. So regardless of the content, if an argument has a certain form, it is automatically valid.<br>
78
Modus Ponens If it rains, my car is wet.
It rains.
Therefore, my car is wet.
To make our lives easier, let’s put it like this:
If R, then W.
R.
Therefore, W.<br>
It rains.
Therefore, my car is wet.
To make our lives easier, let’s put it like this:
If R, then W.
R.
Therefore, W.<br>
79
Modus Ponens is a conditional argument. The statement “If R” is the antecedent. The statement “Then W” is the consequent. Modus Ponens means “Affirming the antecedent.”
Any argument that has such a form is valid regardless of its subject matter.<br>
Any argument that has such a form is valid regardless of its subject matter.<br>
80
Modus tollens There is an old saying, “A man’s modus ponens is another man’s modus tollens.” (Denying the consequent)
If it rains, my car is wet.
My car is not wet.
Therefore, it does not rain.
In letter form:
If R, then W.
Not W.
Therefore, Not R.<br>
If it rains, my car is wet.
My car is not wet.
Therefore, it does not rain.
In letter form:
If R, then W.
Not W.
Therefore, Not R.<br>
81
Barbara All cows are ruminating animals.
All ruminating animals are docile.
All cows are docile.
In letter form:
All C are R.
All R are D.
All C are D.<br>
All ruminating animals are docile.
All cows are docile.
In letter form:
All C are R.
All R are D.
All C are D.<br>
82
Disjunctive Syllogism You wear glasses or contact lenses.
You do not wear glasses.
You wear contact lenses.
In letter form:
Either G or L.
Not G.
L.<br>
You do not wear glasses.
You wear contact lenses.
In letter form:
Either G or L.
Not G.
L.<br>
83
Here are three more forms, but they are always invalid<br>
84
Undistributed Middle All cows are ruminating animals.
All sheep are ruminating animals.
All sheep are cows.
In letter form:
All C are R.
All S are R.
Therefore, all S are C.<br>
All sheep are ruminating animals.
All sheep are cows.
In letter form:
All C are R.
All S are R.
Therefore, all S are C.<br>
85
Denying The Antecedent If you study, then you pass.
You do not study.
You do not pass.
In letter form,
If S, then P.
Not S.
Therefore, not P.<br>
You do not study.
You do not pass.
In letter form,
If S, then P.
Not S.
Therefore, not P.<br>
86
Affirming The Consequent If it rains, then my car is wet.
My car is wet.
Therefore, it rains.
In letter form,
If R, then W.
W.
R.<br>
My car is wet.
Therefore, it rains.
In letter form,
If R, then W.
W.
R.<br>
87
2. induction<br>
88
INDUCTION is a process of reasoning from premises to a probable conclusion.
The premises do not lead necessarily to the conclusion.
Given the premises, conclusion is likely to be the case.
It cannot ever be said that it doesn’t follow at all.
It cannot ever be said that it follows necessarily.<br>
The premises do not lead necessarily to the conclusion.
Given the premises, conclusion is likely to be the case.
It cannot ever be said that it doesn’t follow at all.
It cannot ever be said that it follows necessarily.<br>
89
A Sound argument, obviously, is a good argument: All true premises, conclusion follows by logical necessity.
An inductive argument cannot be valid or sound. It can be weak or strong.
A good inductive argument is called “cogent.”
Strong + True Premises = Cogent
Strong + At Least One False Premise = Uncogent
Weak = Uncogent<br>
An inductive argument cannot be valid or sound. It can be weak or strong.
A good inductive argument is called “cogent.”
Strong + True Premises = Cogent
Strong + At Least One False Premise = Uncogent
Weak = Uncogent<br>
90
INDUCTION There are three kinds of inductive arguments:
Inductive Generalizations.
Arguments from Analogy.
Causal Arguments.<br>
Inductive Generalizations.
Arguments from Analogy.
Causal Arguments.<br>
91
1. INDUCTIVE GENERALIZATION To move from a sample to a general conclusion about a population.
This desk is brown.
That desk is brown.
Therefore, all desks are brown.<br>
This desk is brown.
That desk is brown.
Therefore, all desks are brown.<br>
92
2. ARGUMENTS FROMANALOGY Using an analogy between two or more things (also people, events, etc.) in order to support a conclusion about one of them. Complex mechanisms, watches, for example, were designed by a mind.
The bacterial flagellum is a complex mechanism.
Therefore, the bacterial was designed by a mind.<br>
The bacterial flagellum is a complex mechanism.
Therefore, the bacterial was designed by a mind.<br>
93
3. CAUSAL ARGUMENT An arguments that contains a causal statement as either a premise or the conclusion. Causal Explanation:
Reduction in swelling causes relief of pain.
There is relief of pain.
Therefore, the swelling in my arm has gone down. Causal Prescription:
Listening to classical music makes you relax.
If you desire relaxation, you should listen to classical music. Causal Conclusion:
Whenever I eat tofu, I get phlegm in my throat.
Therefore, eating tofu causes the production of phlegm Causal Prediction:
Smoking causes cancer..
You smoke.
You (likely) will get cancer.<br>
Reduction in swelling causes relief of pain.
There is relief of pain.
Therefore, the swelling in my arm has gone down. Causal Prescription:
Listening to classical music makes you relax.
If you desire relaxation, you should listen to classical music. Causal Conclusion:
Whenever I eat tofu, I get phlegm in my throat.
Therefore, eating tofu causes the production of phlegm Causal Prediction:
Smoking causes cancer..
You smoke.
You (likely) will get cancer.<br>
94
DEDUCTIVE
Conclusion follows necessarily or not at all VALID: Given the premises, the conclusion follows necessarily. SOUND: A deductively valid argument with all true premises
THIS IS A GOOD ARGUMENT UNSOUND: A deductively valid argument with at least one false premise. NOT A GOOD ARGUMENT INVALID: Given the premises, the conclusion does not follow at all—even if the premises are true. NOT A GOOD ARGUMENT INDUCTIVE
Conclusion always follows probably UNCOGENT:
True premises but weak. Weak means given the premises, the conclusion is not likely to be true. NOT A GOOD ARGUMENT UNCOGENT: False premises but strong. Strong means given the premises, the conclusion is very likely to be true. NOT A GOOD ARGUMENT COGENT: Strong plus all true premises. THIS IS A GOOD ARGUMENT<br>
Conclusion follows necessarily or not at all VALID: Given the premises, the conclusion follows necessarily. SOUND: A deductively valid argument with all true premises
THIS IS A GOOD ARGUMENT UNSOUND: A deductively valid argument with at least one false premise. NOT A GOOD ARGUMENT INVALID: Given the premises, the conclusion does not follow at all—even if the premises are true. NOT A GOOD ARGUMENT INDUCTIVE
Conclusion always follows probably UNCOGENT:
True premises but weak. Weak means given the premises, the conclusion is not likely to be true. NOT A GOOD ARGUMENT UNCOGENT: False premises but strong. Strong means given the premises, the conclusion is very likely to be true. NOT A GOOD ARGUMENT COGENT: Strong plus all true premises. THIS IS A GOOD ARGUMENT<br>
95
TEST YOUR KNOWLEDGE<br>
96
All dogs have 4 legs.
All tables have 4 legs.
Therefore, all dogs are tables.
Dang I’m a smart dog!<br>
All tables have 4 legs.
Therefore, all dogs are tables.
Dang I’m a smart dog!<br>
97
All actors are robots.
Tom Cruise is an actor.
Therefore, Tom Cruise is a robot.<br>
Tom Cruise is an actor.
Therefore, Tom Cruise is a robot.<br>
98
All actors are robots.
Tom Cruise is a robot.
Therefore, Tom Cruise is an actor.<br>
Tom Cruise is a robot.
Therefore, Tom Cruise is an actor.<br>
99
1. All female TV hosts are successful TV hosts.
2. Oprah Winfrey is a successful TV host.
3. Therefore, Oprah Winfrey is a female TV host.<br>
2. Oprah Winfrey is a successful TV host.
3. Therefore, Oprah Winfrey is a female TV host.<br>
100
All things with 3 sides are triangles.
Some things with 3 angles are triangles.
Therefore, some things with 3 angles are things with 3 sides.<br>
Some things with 3 angles are triangles.
Therefore, some things with 3 angles are things with 3 sides.<br>
101
Things with 3 sides become ants
Triangles become insects
Things with 3 angles become things that fly Let’s change terms:<br>
Triangles become insects
Things with 3 angles become things that fly Let’s change terms:<br>
102
All ants are insects.
Some things that fly are insects.
Therefore, some things that fly are ants. INVALID<br>
Some things that fly are insects.
Therefore, some things that fly are ants. INVALID<br>
103
Eating soap gives you stomachache.
You are eating soap.
Your stomach will ache.<br>
You are eating soap.
Your stomach will ache.<br>
104
Whenever I turn the knob right the volume increases.
Therefore, turning the knob right causes the volume to increase.<br>
Therefore, turning the knob right causes the volume to increase.<br>
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All bachelors are males.
Joe is a male.
Therefore, Joe is a bachelor.<br>
Joe is a male.
Therefore, Joe is a bachelor.<br>
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40% of all SUNY teachers we interviewed are underpaid.
So, all SUNY teachers are underpaid.<br>
So, all SUNY teachers are underpaid.<br>
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The moon is made of cheese.
Cheese can be eaten.
Therefore, the moon can be eaten.<br>
Cheese can be eaten.
Therefore, the moon can be eaten.<br>
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Logical Fallacies<br>
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Logical Fallacies Logical Fallacy are instances of bad or poor reasoning.
Fallacies are FORMAL or INFORMAL:
A formal fallacy is an error that can be seen clearly. For example:
If Taylor is the president of the US, she must be 35 or older.
She is 35.
Therefore, she is the president of the US.<br>
Fallacies are FORMAL or INFORMAL:
A formal fallacy is an error that can be seen clearly. For example:
If Taylor is the president of the US, she must be 35 or older.
She is 35.
Therefore, she is the president of the US.<br>
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According to Gordon Ramsey, eating meat is morally permissible.
According to Einstein, abortion is always immoral. Appeal to Authority: when you claim that your conclusion is true because some irrelevant or is biased authority.<br>
According to Einstein, abortion is always immoral. Appeal to Authority: when you claim that your conclusion is true because some irrelevant or is biased authority.<br>
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Jeremiah argues: Slavery is morally permissible. Why? Because virtually everyone considers slavery a moral practice.
People have believed in God for millennia. I don’t see how so many people could be wrong. Therefore, God exists. Appeal to the People: when your conclusion is based on the majority.<br>
People have believed in God for millennia. I don’t see how so many people could be wrong. Therefore, God exists. Appeal to the People: when your conclusion is based on the majority.<br>
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Well, it’s time for a decision. Either you contribute $10 to our environmental fund, or you are on the side of environmental destruction?
~ Either you drove here, or you walk. So, if you didn’t walk, you must have driven.
~ Either we enforce death penalty, or we find convicted murderers back out on the streets. We cannot have murderers out on the streets. Therefore, we must enforce the death penalty. False Dichotomy<br>
~ Either you drove here, or you walk. So, if you didn’t walk, you must have driven.
~ Either we enforce death penalty, or we find convicted murderers back out on the streets. We cannot have murderers out on the streets. Therefore, we must enforce the death penalty. False Dichotomy<br>
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If God is love and love is blind, and Stevie Wonder is blind. Then Stevie Wonder is God!
The doctor told me I need amino acids. But acids corrode your stomach. So I am not eating amino acids.
All feathers are light. Whatever is light cannot be dark. Therefore, feathers cannot be dark.
Logic is the study of arguments. My parents argue a lot. Therefore, I can learn logic by listening to my parents argue. Equivocation: when the conclusion rests on the equivocal use of a word or phrase.<br>
The doctor told me I need amino acids. But acids corrode your stomach. So I am not eating amino acids.
All feathers are light. Whatever is light cannot be dark. Therefore, feathers cannot be dark.
Logic is the study of arguments. My parents argue a lot. Therefore, I can learn logic by listening to my parents argue. Equivocation: when the conclusion rests on the equivocal use of a word or phrase.<br>
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Each member of the orchestra is excellent; therefore the orchestra is excellent.
Drinking this glass of whiskey cannot harm me, so how can drinking harm me?
Every brick of that house is relatively light. Therefore, the house must be light. Composition: if it applies to the individual it applies to the whole.<br>
Drinking this glass of whiskey cannot harm me, so how can drinking harm me?
Every brick of that house is relatively light. Therefore, the house must be light. Composition: if it applies to the individual it applies to the whole.<br>
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The union voted to strike. Therefore, each member voted to strike.
Humans are the only animals capable of philosophical thinking. Therefore, every human being is capable of philosophical thinking. Division: if it applies to the whole it applies to the individual.<br>
Humans are the only animals capable of philosophical thinking. Therefore, every human being is capable of philosophical thinking. Division: if it applies to the whole it applies to the individual.<br>
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My doctor told me I should lose some weight. But why should I listen to him? He’s fat!
Professor Dawkins told us about the theory of evolution. But he’s a Godless atheist! Therefore, evolution is false.
Rousseau’s theory of education? That monster dares speak of education! He abandoned his children and the tramp with whom he made them.” Ad Hominem: when you attack the person rather than the argument.<br>
Professor Dawkins told us about the theory of evolution. But he’s a Godless atheist! Therefore, evolution is false.
Rousseau’s theory of education? That monster dares speak of education! He abandoned his children and the tramp with whom he made them.” Ad Hominem: when you attack the person rather than the argument.<br>
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We should oppose same sex marriage because if we allow it then eventually people would demand to marry animals.
We cannot unlock our child from the closet because if we do, she will want to roam the house. If we let her roam the house, she will want to roam the neighborhood. If she roams the neighborhood, she will get picked up by a stranger in a van, who will sell her in a sex slavery ring in some other country. Therefore, we should keep her locked up in the closet. Slippery Slope: a conclusion is dismissed because it leads to a chain of undesirable consequences.<br>
We cannot unlock our child from the closet because if we do, she will want to roam the house. If we let her roam the house, she will want to roam the neighborhood. If she roams the neighborhood, she will get picked up by a stranger in a van, who will sell her in a sex slavery ring in some other country. Therefore, we should keep her locked up in the closet. Slippery Slope: a conclusion is dismissed because it leads to a chain of undesirable consequences.<br>
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Paranormal activity is real because I have experienced what can only be described as paranormal activity.
Objects that are less dense than water will float because such objects won’t sink in.
The Book of God is divinely inspired because it says so right in the third chapter: “All scripture is divinely inspired.”
Of course smoking causes cancer. The smoke from cigarettes is a carcinogen. Begging the Question: when the premises assume the truth of the conclusion.<br>
Objects that are less dense than water will float because such objects won’t sink in.
The Book of God is divinely inspired because it says so right in the third chapter: “All scripture is divinely inspired.”
Of course smoking causes cancer. The smoke from cigarettes is a carcinogen. Begging the Question: when the premises assume the truth of the conclusion.<br>
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The theory of evolution says that man comes from monkeys. But how come monkeys don’t give birth to human babies? The theory of evolution is absurd!
We should stop using animals for scientific research.
So you doesn’t care about the progress of medicine?
Zoe: What is your view on God?
Mike: I don’t believe in any gods.
Zoe: Oh, so you think that we are here by accident, and all this design in nature is pure chance, and the universe just created itself? Straw Man: when you misinterpret or misrepresent the position of your opponent.<br>
We should stop using animals for scientific research.
So you doesn’t care about the progress of medicine?
Zoe: What is your view on God?
Mike: I don’t believe in any gods.
Zoe: Oh, so you think that we are here by accident, and all this design in nature is pure chance, and the universe just created itself? Straw Man: when you misinterpret or misrepresent the position of your opponent.<br>
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Teaching teenagers to stay away from drinking by getting them drunk is like teaching gun safety by playing Russian roulette.
To say humans are immortal is like saying a car can run forever.
If complicated mechanisms require a maker, then the universe must have a maker as well. False Analogy: when your analogy is bad!<br>
To say humans are immortal is like saying a car can run forever.
If complicated mechanisms require a maker, then the universe must have a maker as well. False Analogy: when your analogy is bad!<br>
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There is a lot of commotion regarding saving the environment. We cannot make this world an Eden. What will happen if it does become Eden? Adam and Eve got bored there!
The crime in this city, has, in fact increased lately. However, let's consider that the weather has changed as well. Things change over time. Sometimes they are linked, sometimes they are not, but only time will tell. The Red Herring: when you are moving the target.<br>
The crime in this city, has, in fact increased lately. However, let's consider that the weather has changed as well. Things change over time. Sometimes they are linked, sometimes they are not, but only time will tell. The Red Herring: when you are moving the target.<br>
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The end.questions?<br>