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NYC COLLEGE OF TECHNOLOGY Intro to Philosophy PHIL 2101 Prof. Carlo Alvaro

LOGICLOGIC – DEFINITION, AND MORE

Logic is the Study of the principles and concepts of good reasoning.

This implies that there is a distinction between good and bad reasoning.

Also, logicians, people who study logic, are not interested in HOW people reason, those are psychologists. Logicians are interested in the principles of reasoning.

THE THREE “LAWS OF THOUGHT”

Early Logicians defined logic as the “science of the laws of thought” and that there are three basic laws we must obey to think correctly:

1. The principle of identity: This asserts that if any statement is true, then it is true!2. The principle of non-contradiction: This asserts that no statement can be both true and

false.3. The principle of excluded middle: this asserts that any statement is either true or false.

History of LogicAristotle (384-322 B.C.E.) invented logic. He used letters for terms, he created syllogistic logic, which studies arguments like these

All humans are mortal. = All H are M.

All Greeks are humans. = All G are H.

Therefore All Greeks are mortal. = All G re M.

This argument is valid because of its structure. So any argument with the same structure is valid.

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Aristotle studied the logic of possibility and necessity.

Stoics continued Aristotle’s work and in the Medieval Period many thinkers developed ways to teach Aristotle’s system of logic. During the Enlightenment many philosophers would just agree that nothing significant was invented in logic after Aristotle. Leibniz (1646-1716), however, anticipated modern logic, proposing a concept of symbolic language, but his work was published after George Boole (1815-1864).

In 1879, Gottlob Frege (1848-1925) invented modern logic. He created more ways to express logic through symbols and operators. His project was to show that arithmetic is reducible to logic. Some sets, such as the set of all teacups, or of all cats are not members of themselves. The set of all teacups is not a teacup and the set of all cats is not a cat. Other sets, such as the set of all non-teacups, or the set of all abstract objects are members of themselves because the set of all non-teacups is a non-teacup and the set of all abstract objects is an abstract object. Now, consider the set of all sets that are not members of themselves “R.” If R is a member of itself, then by definition it must not be a member of itself. Similarly, if R is not a member of itself, then by definition it must be a member of itself. Frege’s life work was destroyed! This is known as the Russell’s Paradox. Russell and Whitehead developed a system that fixed this problem.

These new developments propelled logic forward to new territories that Aristotle would be impressed. Systems like truth tables were invented. Modern Logic was important in the development of computers. Also the most important aspect of logic is modal logic dealing with necessary and possible.

The distinction between analytic and synthetic judgments, and by that between a priori and a posteriori knowledge.

Analytic and Synthetic Judgments

Any sentence has a Subject and a Predicate.

A simple subject/predicate sentence can be either universal, “all bachelors are unmarried,” or particular, “this chalk is white” is Analytic if and only if the predicate concept is “contained in” the subject concept.

To analyze something is to determine how it is constructed out of its constituent parts. An analysis of a concept is like a definition of the concept. For example, we might discover that something fits the concept bachelor if and only if it is an unmarried male person. In this case we can say that the concept bachelor contains such concept as being unmarried. So a judgment is analytic if analysis of the subject-concept reveals that it contains the predicate-concept.

A judgment is synthetic if and only if it is not analytic. Or, a judgment is synthetic just when the predicate concept is not contained in the subject concept. For example, “all bachelors are tall,” “the Sun will rise tomorrow,” or “the children are playing in the playground,” are synthetic judgments.

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A Priori and A Posteriori Knowledge:

Consider these two statements:

1. All bachelors are unmarried.2. Some bachelors are happy.

While we know both to be true, how we know differs.

A judgment is knowable a priori if and only if it can be justified independently of experience. A judgment is a posteriori if it cannot be known without recourse to experience. Arguably, the truths of mathematics (2 + 2 = 4) and logic (if George will go only if John will go, and George will go, then John will go) are a priori. We do not need empirical evidence in order to know that they are true.

Most judgments of particular fact, however, are a posteriori. I cannot know that a particular room is more than 10’ wide without some sort of experience, for example the experience of measuring the room with a tape measure.

Can we have synthetic a priori knowledge?

Immanuel Kant says yes.

Consider, for example, our knowledge that 7+5=12 and that the interior angles of any triangle add up to a straight line. These (and similar) truths of mathematics and geometry are synthetic judgments: the concept “the sum of the interior angles” is not contained in the concept of a triangle. Yet, clearly, such truths are known a priori, since they apply with strict and universal necessity to all of the objects of our experience, without having been derived from that experience itself.

In 1951, Willard Van Orman Quine published the essay “Two Dogmas of Empiricism” in which he argued that the analytic–synthetic distinction is untenable. The argument at bottom is that there are no “analytic” truths, but all truths involve an empirical aspect.

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Analytic Synthetic

A Priori X ?A Posteriori X


Quine argues:

Analytic propositions – propositions grounded in meanings, independent of matters of fact.

Synthetic propositions – propositions grounded in fact.

The notion of an analytic proposition requires a notion of synonymy, but establishing synonymy inevitably leads to matters of fact – synthetic propositions.

What is knowledge?Is knowledge only what is true or rather what is useful? But is it what is useful always true? Take mathematics. We agree that it is a form of knowledge. But is 2+2=4 really knowledge or a tautology? What can 2+2=4 tell us about the world?

Religion: many have justified belief in claiming knowledge of the existence of a god. Others, in a similar way, have sound justification to claim that there isn’t any god.

Then to what extent is it possible for a given subject or entity to be known? One view is the objection that there is very little or no knowledge at all—skepticism. If you think you can clearly define knowledge, then you know not what knowledge is.

Before Galileo, earth was “known” to be at the center of the universe. Today we “know” better—but do we? What puts us in a better position? If knowledge is linked with truth, what is the best instrument with which to acquire truth? Is it science? Is it religion?

We saw the distinction between empiricism and rationalism. Which of the two views affords us knowledge?

Knowledge that, knowledge how: in epistemology in general, the kind of knowledge in which philosophers are interested is propositional knowledge, AKA “knowledge that.”

Example: The way in which we are able to see atoms is by using the “Scanning Tunneling Microscope” (STM). This type of microscope has an extremely sensitive “probe” with a very fine tip that, so to speak, feels the bumps caused by atoms. These “bumps” then are converted by a computer into a picture showing the individual atoms.

When the probe of the microscope is brought close to the surface of the sample, there is an interaction between the electron cloud and the tip of the probe. The question that follows is obvious:

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What are those bumps, real atoms or images produced by a microscope that was built by its inventor to see those images?

Atoms are thousands of times smaller than the smallest visible light waves, but there is so much evidence for atoms, and the success of many theories depend on the fact that we know so much about atoms. Now, some philosophers may object that such devices as the STM are made appositely to see what we want to see? But others say that if atoms do not exist, then it would seem that our theories work accidentally!

Traditional Theory of knowledge: Many epistemologists hold the Justified True Belief (JTB) account of knowledge: the claim that knowledge can be conceptually analyzed as justified true belief.

A subject S knows that a proposition P is true if and only if:

1. P is true2. S believes that P is true, and3. S is justified in believing that P is true

Is Justified True Belief (JTB) knowledge? Consider these 3 scenarios:

I. Your roommate is watching TV in the kitchen. You’re in the bathroom preparing for work. You need to know the time and so you get out of the bathroom and see the time as it appears on the lower right corner of the TV set, which reads 2:15 P.M. You’re late for work. You get dressed quickly and zoom out. Now what you don’t know is that your friend was playing a tape. It just so happened that the time in the video precisely coincided with the real time. Now, do you know the time?

1. It is true that the time is 2:15.2. You believe that the time is 2:15, and,3. You are justified in believing that the time is 2:15.

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LOGIC THE SCIENCE OF ARGUMENTS

Different sciences, like biology, mathematics, etc. study their respective subject matters. Logic studies arguments. Arguments are the subject matter of logic.

In logic, an argument is a piece of reasoning used to show or express or prove a point; that point, whatever it may be, is supported by sub-points, which are statements.

For example:

All humans are mortal. My logic prof. is human.

Therefore, my logic prof. is mortal.

This is a classic example of an argument. A point is expressed—namely, that logic prof. is mortal. This is called conclusion. The conclusion is supported by certain statements, All humans are mortal and my logic prof. is human.

ARGUMENT DEFINITION: An argument is a group of premises (at least one premise) in support of a conclusion.

OR

A group of statements, one of which is claimed to follow from the others.

PREMISE DEFINITION: A premise is a statement capable of being true or false. “Fetch me a bagel!” is not a premise. “Joe is my dog.” is a premise.

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CONCLUSION DEFINITION: A conclusion is also a statement capable of being true or false; in addition, it is the main point of the argument, that is, the statement that is claimed to follow from other premises (statements).

HOW TO UNDERSTAND/RECOGNIZE AN ARGUMENT

To understand an argument you must first pick out the conclusion. To pick out the conclusion ask yourself, “What’s the main point? What does the speaker want to persuade me to believe?”

Also you can spot the conclusion as it is often preceded by certain clue words: Therefore, thus, it must be deduced that, so, consequently…

On the other hand, premises often begin with these words: Since, because, for, given that…

ARGUMENT FORM

Arguments are given by people in the form of a speech. We will study textbook examples of arguments to facilitate our discussion.

Also, the arguments I will present will have numbered premises. Conclusions will be differentiated by other premises with a straight line that separates them from premises, like this:

1. All flowers are plants. (Premise 1)2. All Roses are flowers. (Premise 2)_______________________________

3. Therefore, all roses are plants. (Conclusion)

Exercise: Argument form – Determine Arguments, put them in argument form

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SUPPLYING MISSING PARTS – ENTHYMEMES

What’s missing?

An argument missing a premise, or a conclusion, is an enthymeme. Eg:

1. All chemists are scientists. 1. If you wake up late, you’ll miss your train.

2. So Joe is a scientist. OR 2. And as usual, you woke up late.

Exercise: Supply Missing Parts

DIAGRAMMING ARGUMENTS

Another technique to identify arguments is diagramming them. To diagram, read it through and then number each statement.

e.g.: Joe was promoted to VP; therefore, he will move to DC.

Number Like such:

(1) Joe was promoted to VP.(2) He will move to DC.

The above example is called “Single support” because the conclusion is directly supported by the premise.

Now draw an arrow from the statement to the conclusion:

(1)

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(2) e.g.: If Joe is promoted to VP, he will move to DC. He was promoted; therefore, he will move to DC.

Number Like Such:

(1) If Joe is promoted to VP he will move to DC.(2) He was promoted.(3) Therefore he will move to DC.

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In this case you have a “Joint Support” (if…then)

(1) + (2)

|

(3)

Let’s do it again…

e.g.: Cats make good pets because they are affectionate, they’re clean, they’re entertaining, and they do well in apartments.

(1) Cats make good pets...(2) They’re affectionate,(3) They’re clean,(4) They’re entertaining,(5) They do well in apartments.

This is an example of “Independent Support.”

(2)(3) (4) (5)

|

(1)One More Time…

e.g.: Cats make good pets because they are affectionate, they’re clean, they’re entertaining, and they do well in apartments. So if you want a good pet, you should get a cat.

(1) Cats make good pets...(2) They’re affectionate,(3) They’re clean,(4) They’re entertaining,(5) They do well in apartments.(6) If you want a good pet, you should get a cat.

This is an example of “Extended Argument”

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(2) (3) (4) (5)

|

(1)

|

(6)

Last one and then you do it…

e.g.: Cats make good pets and cats make good anatomical subjects. Therefore, some good pets make good anatomical subjects. Since good anatomical subjects are in high demand in medical schools, it follows that some good pets are in high demand in medical schools.

(1) Cats make good pets,(2) Cats make good anatomical subjects,(3) Therefore some good pets make good anatomical subjects. (4) Since good anatomical subjects are in high demand in medical schools, it follows that(5) Some good pets are in high demand in medical schools.

(1) + (2)

|

(3) + (4)

|

(5)The above argument is also an extended argument: there is an argument within an argument. You see that (1) and (2) support conclusion (3). Then (3) is combined with (4) to support (5)

Exercises: Diagramming arguments

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IN SEARCH FOR A GOOD ARGUMENT

What’s a good argument? Good arguments have

(A) A conclusion that follows from the premises and(B) The premises are true.

What does it mean to follow? 2 ways to follow: deductive validity or inductive strength.

DEDUCTION VS. INDUCTIONArguments can be deductive or inductive. A deductive argument can be valid or invalid; and a valid argument can be sound or unsound. An inductive argument can be weak or strong.

An argument is called DEDUCTIVE when its conclusion follows NECESSARILY—by logical necessity. Deductive arguments may be valid or invalid.

DEDUCTIVE + VALID

1. If I am eating I have food.2. I am eating.3. Therefore I have food.

Given premises 1 and 2, the conclusion, 3, is necessary. If you deny (3) you contradict yourself.

1. If it rains my car is wet.2. It rains.3. Therefore my car is wet.

1. People from France speak French2. Marc is from France.

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3. Therefore, he speaks French

1. All bachelors are males.2. Joe is a bachelor.3. Therefore he is a male.

1. A human fetus has a brainwave after 25 weeks.2. A human fetus with a brain wave is a person.3. Killing a person is morally wrong.4. Therefore, killing a fetus after 25 weeks is morally wrong.

1. All animals have teeth.2. Dogs are animals.3. Therefore, dogs have teeth.

Note that an argument may be deductively valid, yet have one or more false premises.Premise (1) is false because birds, and octopi, shrimp, etc. are not teethed animal. The second argument has a false premise and false conclusion:

1. The moon is made of marshmallow.2. Marshmallow is edible.3. Therefore, you can eat the moon.

Now, what is an INVALID argument? A deductive argument is INVALID when its conclusion does not follow at all.

DEDUCTIVE + INVALID1. If it rains my car is wet.2. My car is wet.3. It follows that it rains.

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1. Dogs have teeth.2. Dogs are animals.3. So, we must deduce that all animals have teeth.

1. If you are eating you have food.2. You have food. 3. Therefore you are eating!

1. All bachelors are males2. Joe is a male.3. It follows then that Joe is a bachelor.

1. All politicians are liars. 2. All used car salesmen are liars. 3. Therefore all politicians are used car salesmen.

1. All ants are insects.2. All mosquitoes are insects.3. Therefore, all ants are mosquitoes.

The above arguments are INVALID because their conclusions are not granted by the premises; or, they neither follow necessarily nor probably—they just don’t follow!

Next, deductive arguments can be sound or unsound.

DEDUCTIVE + VALID + SOUND

1. All humans are mortal.2. Nancy is human.3. Therefore, Nancy is mortal.

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1. All us presidents are politicians2. Obama is a US president.3. Therefore Obama is a politician.

1. 5 is greater than 3.2. 3 is greater than 2.3. Therefore, 5 is greater than 2.

1. All physical objects occupy space.2. My book is a physical object.3. Therefore, my book occupies space.

1. Citytech is either in China or In Brooklyn.2. Citytech is not in China.3. Therefore, Citytech is in Brooklyn.

The foregoing arguments are DEDUCTIVE because their conclusions follow by logical necessity and not probably. Hence, they are VALID. Furthermore, they are SOUND because their premises are true.

DEDUCTIVE + VALID + UNSOUND

1. If January has 33 days, the 33rd is the last day.2. January has 33 days.3. Therefore, the 33rd is the last day.

1. All unicorns have wings.2. Juju is a unicorn.3. Therefore, Juju has wings.

1. All living things can fly.2. Women are living things.3. Therefore, women can fly.

1. All felines have six legs.2. Tigers are felines.3. Therefore, tigers have six legs.

Notice that the conclusion to these arguments is necessary. The premises are related: one leads to the other; GIVEN THE PREMISES, the conclusion follows from the premises necessarily and not

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probably. So, these are deductively valid arguments. But they are unsound because soundness requires true premises.

INDUCTIONOn the other hand, INDUCTIVE arguments work differently. The conclusion to an inductive argument can be strong or weak, depending on the circumstances, but never 100% true or 100% false. There are 2 kinds of inductive arguments: Inductive Generalizations and Arguments By Analogy.

INDUCTIVE GENERALIZATION

To move from a sample to a general conclusion about a population.

1. This desk is brown.2. That desk is brown.3. Therefore, all desks are brown

1. The last ten times I played poker I won $.2. I’m playing poker tonight.3. Therefore I’ll win $.

4. The last ten times I played poker I won $.5. I’m playing poker tonight.6. Therefore I will not win $.

NOTICE THAT EVEN IF I DENY THE CONCLUSION, UNLIKE IN DEDUCTIVE ARGUMENTS, THE CONCLUSION IS STILL POSSIBLE!

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1. 90 % of Citytech students are females.2. Therefore, the first person I’ll run into in the hallway is a female.

1. There are 20 cards in the deck and that includes 13 aces.2. I need to draw an ace to win.3. Therefore, I’ll win.

1. There are 1000 marbles in a jar.2. I take one and it’s red.3. Therefore they’re all red.

INDUCTIVE STRENGTH

1. There are 1000 marbles in a jar.2. I take 980 and they’re red.3. Therefore they’re all red

1. I’ve seen things fall to the ground when dropped many times.2. I’m about to drop this object.3. Therefore, it will fall to the ground.

ARGUMENTS BY ANALOGY

Comparing two or more things in order to support a conclusion about one of them.

1. I read a book by Stephen King and it was very entertaining.2. I also watched a movie based on one of his books and was entertaining.3. Therefore his latest book must be entertaining as well.

1. Any mechanism like a watch is not the product of nature but a maker.2. The world is a complex mechanism.3. So the world has a maker, and that is God.

1. I bought a Ford Focus and it performs well. 2. So, if you want a car that performs well, you need a Ford Focus.

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1. The state is like family.2. You must respect family.3. Therefore, you must respect the state.

…AND MORE

All observed people are right-handed; therefore all the people are right-handed. (Inductive generalization)

All the dogs that have been observed can bark, therefore all the dogs can bark. (Simple induction)

John and Joe are friends. John likes to sing, write and read. Joe likes to sing and write. Therefore one assumes that Joe also likes to read. (Argument from analogy)

A few episodes of a particular sitcom make you laugh, and you conclude that the said sitcom is very funny.

Look at the patterns below. Can you draw the next figure or next set of dots using inductive reasoning?

People are naturally inclined to see patterns in nature. But “How do you interpret these patterns?” is the question. So, one may be tempted to say that logically the next pattern should have 9 dots or 12 if multiply by 2. However, notice that one dot is always placed between and above two dots. Also, the next figure always has one more dot at the very bottom row

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APPLIED INDUCTION


Keeping this in mind, your next figure should look like this:

Causal Argument

Arguments that rely on the concept of causality.

Causal Arguments contain causal statements as either a premise or the conclusion. Causal statements say that A is the cause of B and B is caused by A.

Sufficient VS Necessary Condition.

Oxygen is necessary for combustion, but not sufficient.

It is not always clear what the cause is.

In November 2003, a man resisting arrest died shortly after being beaten into submission by police officers in Cincinnati, Ohio. The struggle, you might say, is the primary “Cause” of his death. But what is really the cause? That is, what made him die? Lack of oxygen, damage of brain?

Another example: Persons who leave school before the age of 16 are 5 times more likely than university graduates to die from heart attack. And the death rate within one year of a heart attack is 3.5% for college graduate and 20% for those with fewer than 8 years of formal schooling. What is really the cause? Poor education is certainly part of it.

Increased stress causes increased risk of heart attack.

Drinking alcohol during pregnancy cause birth defects.

Smoking causes cancer.

Eating heavy food causes stomachache.

Jogging cause my side pain.

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The conflict over slavery caused the Civil War.

Mill’s MethodsJohn Stewart Mill (1806 – 1873) describes 5 methods for identifying causes and effects: METHODS OF AGREEMENT, DIFFERENCE, CONCOMITANT VARIATION, RESIDUE, and the joint method of AGREEMENT AND DIFFERENCE.

1. THE METHOD OF AGREEMENT

This method tells us to look at antecedent circumstances. The cause of an event is that antecedent circumstance common to all cases in which that event occurs.

Explanation: Suppose 3 friends eat at the same restaurant and an hour later they get sick. The method of agreement suggests that we identify the cause by looking at which food in common was eaten among the three. Say that all three ate fish, then the cause of their sickness is fish.

You can see that this method is not very reliable. What is nothing is in common?

2. THE METHOD OF DIFFERENCE

According to this method we can find out the cause of an event by looking at the antecedent event that is present when something occur and we compare to those events that lack that antecedent event.

Explanation: Suppose you touch the TV antenna and the image gets clear. If you don’t touch the antenna the image is blurry. So by comparison, we infer that touching the antenna is the cause of clear images. Also, if you made the same soup with the same ingredients many times and then added a new ingredient, you infer that the cause of, say, a bitter taste is the new ingredient.

3. THE METHOD OF CONCOMITANT VARIATION

Things and people exhibit variation, they change. Often we observe that such variations are in concomitance with variations in other circumstances:

Explanation: If a variation in a certain event E coincide with another variation in phenomenon P, then it is probable that E and P are causally related.

~ The more you exercise the stronger you get.

~ The higher the humidity, the longer it takes for my clothes to dry.

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4. THE METHOD OF RESIDUE

This method suggest that to know the cause of a certain phenomenon we need to subtract causes that are known from previous induction, and the residue of a certain phenomenon is the effect of the remaining antecedent.

Explanation: Suppose we investigate the increased incidence of AIDS in a community. Suppose we already know that the AIDS virus is transmitted through exchange of body fluids. All the cases observed the antecedent circumstances were contaminated needles, unsafe sex, and blood transfusions. We have established that contamination is causal in 65% of cases, unsafe sex 25%. So, we infer that the remaining cases, the residue, are caused by blood transfusions.

Exercises: Identify Types of Arguments

Logical FallaciesOne type of invalid argument is called a Logical Fallacy. These arguments are instances of bad or poor reasoning. The conclusion of a logical fallacy either does not depend on the truth of the premises at all or the conclusion only follows very weakly from the premises. Fallacies can be formal or informal. A formal fallacy is an error in logic that can be seen in the argument’s form without requiring an understanding of the argument’s content. For example, see if you can spot the logical error in this argument:

1. All rats are rodents.2. All squirrels are rodents.______________________3. Therefore, all rats are squirrels.

The error is obvious. Both rats and squirrels are rodents but they are different animals. Consider this other:

1. If it rains, then my car gets wet.2. My car is wet.______________________3. Therefore, it rains.

Again, the error here is to jump to the conclusion without carefully considering the premises. That is to say, my car could be wet for a number of reasons other than that it rained.

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On the other hand, informal fallacies occur for reasons other than structural, and thus require examination of the argument’s content.

Here are some examples:

Ad Hominem

In ethics, you must give objective reasons for your views. Sometimes people get frustrated and attack another person. Often, people attack their opponents rather than their arguments.

Examples:

- My doctor told me I should lose some weight. But why should I listen to him? He’s fat! - Professor Alvaro told us about the theory of evolution. But he neglected to tell us that he’s a

Godless atheist! Therefore, professor Alvaro cannot speak the truth.- Suppose you argue for the moral superiority of suicide for terminally ill patients. I say to

you that I disagree because life is sacred. You respond “You disagree because you are a religious bigot, and religious people are nuts.”

You Too! Fallacy

You too fallacy is committed when a person tries to invalidate your argument by pointing out that you have done or said the very thing that is in question.

Example:Mo: You should not get an abortion; it is morally wrong because it is against nature and is the privation of human life. Jo: Whatever, you got an abortion, you shouldn’t talk.

Reductio ad Absurdum

This is a strategy used to reduce an argument to the absurd by taking a premise and show that it has ridiculous consequences.

Example:

Imagine one argues that nine-day-old embryos are persons. You respond “Ha ha! People are baptized. So you would baptize all embryos that fail to survive to become fetuses?

Equivocation

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Shifting meaning of a key word in an argument results in the fallacy of equivocation.

1. God is love.2. Love is blind.3. Stevie Wonder is blind.4. Thus, Stevie Wonder is God.

Appeal to Emotion (or pity)

The fallacy is committed when one relies on generosity, altruism, or mercy rather than reason.

Example:

Oh, Officer, There's no reason to give me a traffic ticket for going too fast because I was just on my way to the hospital to see my wife who is in serious condition to tell her I just lost my job and the car will be repossessed.

The Red Herring

This is a fallacy in which attention is deliberately moved away from the issue under discussion.

Example:

A: “What we do to animals is morally appalling.”

B: “But what about children starving in the world. That’s a real problem. And where would you get your proteins if all went vegan. And what would happen to the economy…”

Appeal to Authority

You appeal to authority if you back up your reasoning by saying that it is supported by what some authority says on the subject.

Example:

A TV commercial that gives you a testimonial from a famous film star who is against abortion and that suggests you, too, should be against abortion is using a fallacious appeal to authority. The film star—maybe—is an authority on how to act, not on the morality of abortion.

Appeal to Ignorance

The fallacy of “Appeal to Ignorance” occurs when the subject implies that not knowing that a certain statement is true is taken to be a proof that it is false, or vice versa. The fallacy occurs in cases where absence of evidence is not good enough evidence of absence. The fallacy uses an unjustified attempt to shift the burden of proof.

Example:22


There is no evidence that frogs feel pain. They exhibit a certain behavior, but since they have no consciousness they do not feel pain.

Appeal to the People

If you suggest too strongly that someone’s claim or argument is correct simply because it’s what most or everyone believes.

Example:

Eating meat is morally permissible. Look how many people eat meat.

Begging the Question

A form of circular reasoning in which a conclusion is derived from premises that presuppose the conclusion.

Example:

“Killing a human being is morally wrong. But a fetus is not a human being, so it is not wrong to kill a fetus.”

Black-or-White/False Dichotomy

Example:

Well, it’s time for a decision. Either you contribute $10 to our environmental fund, or you are on the side of environmental destruction?

Circular Reasoning/Begging the question

A student argues: “You can’t give me a C. I’m an A student!”

Whatever is less dense than water will float, because such objects won’t sink in.

The Bible asserts that God exists.The Bible is the truth revealed by God.Therefore, God exists.

Slippery Slope

Suppose someone claims that a first step (in a chain of causes and effects, or a chain of reasoning) will probably lead to a second step that in turn will probably lead to another step and so on until a

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final step ends in trouble. If the likelihood of the trouble occurring is exaggerated, the slippery slope fallacy is present.

Example:

We should oppose to homosexual marriage because if we allow it then one day people would demand to marry animals.

Straw Man

Your reasoning contains the straw man fallacy whenever you attribute an easily refuted position to your opponent, one that the opponent wouldn’t endorse, and then proceed to attack the easily refuted position (the straw man) believing you have undermined the opponent’s actual position. If the misrepresentation is on purpose, then the straw man fallacy is caused by lying.

Example:

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!

Appeals to Feelings and Upbringing

How you feel about something or what you were brought up to believe about it does not count as a reason for it.

Examples:

I was brought up drinking milk and eating cheese, so there is nothing wrong with them.

People have been using animals for millennia so I don’t see anything immoral in eating them.

Marriage is between a man and a woman, so gay marriage is wrong!

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