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Arguments in Philosophy

Introduction to Philosophy

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Arguments

■ Philosophy is the art of constructing and evaluating arguments ❑ It’s all about the argument

■ Arguments are meant to be convincing

■ So philosophers must be sensitive to what makes an argument convincing ❑ Or not

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Thinking Critically■ First step: Think Critically

❑ What is the argument trying to say?

❑ Why does the argument succeed, or not?

■ What’s good, bad, or indifferent?

■ The form of the argument ❑ What’s the point?

❑ How do we get to the point?

■ Structure ❑ How do the parts of the argument fit together?

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General Structure■ In general, arguments consist of:

❑ The thesis or position argued for

■ The conclusion

❑ The reasons why the conclusion should be accepted

■ The premises

■ Usually this is written in “standard form”:Premise 1 (Justification)

Premise 2 (Justification)

Therefore, Conclusion (Justification)

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Two kinds of argument

■ In general, there are two kinds of argument: ❑ Deductive Arguments

❑ Inductive Arguments

■ These arguments work (slightly) differently, so they’re evaluated differently

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But let’s be more specific…■ A statement is any unambiguous declarative sentence about a

fact (or non-fact) about the world. ❑ It says that something is (or isn’t) the case.

■ An argument is a series of statements meant to establish a claim.

■ A claim or conclusion is the statement whose truth an argument is meant to establish.

■ A statement’s truth value is either true or false. ❑ All statements have a truth value. A statement is false when

what it says about the world is not actually the case. A statement is true when what it says about the world is actually the case.

■ A premise is a statement that is used in an argument to establish a conclusion.

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Deductive Arguments■ A deductive argument is:

■ VALID if its premises necessarily lead to its conclusion. ❑ That is, if you were to accept that the premises are all

true, you must accept that the conclusion is true.

■ SOUND if it is valid and you accept that all its premises are true.

■ A good, convincing argument is sound.

❑ A bad argument is any other kind of argument.

■ VALIDITY + TRUE PREMISES* = SOUND ❑ *or, at least, accepted premises

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Examples■ All people are mortal. Socrates is a person. Therefore, Socrates

is mortal. ❑ Sound

■ All people are mortal. My dog is mortal. Therefore, my dog is a person. ❑ Invalid.

■ Oranges are green. All green things make me sick. Therefore, oranges make me sick. ❑ Valid. Not sound.

■ Whales know how to play hockey. Therefore, Canadians like winter. ❑ Invalid.

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Notice…■ Validity does not depend on the truth of the

premises. ❑ All people are mortal. My dog is mortal.

Therefore, my dog is a person.

❑ The premises are true. But the argument is still invalid.

■ Soundness does not depend on the truth of the conclusion. ❑ An argument can be bad even if the conclusion is

obviously true.

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Evaluating Deductive Arguments■ Good arguments must be sound.

❑ If you want to accept of an argument, you would have to show both validity and soundness

■ Bad arguments can be bad in two ways: ❑ Invalid

■ You can show that the conclusion does not follow from the premises

❑ Unsound

■ You can show that at least one premise is unacceptable

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Inductive Arguments■ Inductive arguments are not truth preserving

❑ Even in a good inductive argument where the premises are true, the conclusion does not have to be true.

❑ At most, the conclusion is most likely true.

■ Inductive arguments are meant to make conclusions more likely or more acceptable.

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Inductive Arguments

■ An inductive argument is:

■ STRONG if its premises make the conclusion probable

❑ That is, if you were to accept the premises as true, then you would have to accept that the conclusion was probably true

■ COGENT if it is strong and its premises are accepted

■ A good, convincing argument is cogent.

■ STRENGTH + TRUE PREMISES* = COGENT

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Examples■ This cooler contains 30 cans. 25 cans selected at

random contained soda. Therefore, all the cans probably contain soda. ❑ Cogent

■ This cooler contains 30 cans. 3 cans selected at random contained soda. Therefore, all the cans probably contain soda. ❑ Weak

■ Every monkey I’ve seen (over 500) has blue teeth. Therefore, the next monkey I see will probably have blue teeth. ❑ Strong, but not cogent

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Notice…

■ Strength admits of degrees. ❑ An argument can be stronger or weaker

❑ Usually, the more evidence available, the stronger the argument

■ Strength does not depend on the truth of the premises

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Evaluating Inductive Arguments■ Good arguments must be cogent.

❑ If you want to accept of an argument, you would have to show both strength and cogency

■ Bad arguments can be bad in two ways: ❑ Weak

■ You can show that the premises does not make the conclusion more probable

❑ Not cogent

■ You can show that at least one premise is unacceptable

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Argument by Analogy■ One particular kind of inductive argument is an

Argument by Analogy ❑ Comparison of two or more things ❑ Concludes that they share characteristic(s)

■ Because they share other characteristic(s)

❑ Example: ■ Watches exhibit order, function, and design. They were

also created by a creator. The universe exhibits order, function, and design. Therefore, the universe probably was created by a creator.

❑ Evaluated like other inductive arguments

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In Practice…■ Identify the conclusion

❑ What is the claim?

■ Identify the premises ❑ How is the claim supported?

❑ Often, we first have to get rid of anything unnecessary – mere rhetorical flourishes, repetitions, and irrelevancies.

■ Reformulate the argument ❑ Try to put it into standard form

❑ Often, we’ll have to add premises that are implied but not stated.

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In Practice…■ Identify the form of the argument

❑ How are the premises supposed to lead to the conclusion? ■ Deductive? Inductive?

■ Assumptions? Subarguments?

❑ (This will help us add/delete premises)

■ Evaluate the argument ❑ Valid? Sound? ❑ Strong? Cogent? ❑ WHY?

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Example

■ For Death is to be as it were nothing, and to be deprived of all sensation... And if no sensation remains, then death is like a dreamless sleep. In this case, death will be a blessing. For, if any one compares such a night as this, in which he so profoundly sleeps as not even to see a dream, with the other nights and days of his life, and should declare how many he had passed better and more pleasantly than this night, I think that not only a private man, but even the great king himself, would find so small a number that they might be easily counted.

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Example

■ For Death is to be deprived of all sensation... if no sensation remains, then death is like a dreamless sleep. ...death will be a blessing. ...if any one compares such a night [of sleep without dreams]... with the other nights and days of his life, and should declare how many he had passed better and more pleasantly than this night, I think.. [he] would find so small a number...

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Example

■ Death is to be deprived of all sensation. ■ If no sensation remains, death is like a

dreamless sleep. ■ Anyone will consider a dreamless sleep better

than most days and nights. ■ --- ■ Death is a blessing.

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Example

■ Death is to be deprived of all sensation. ■ If no sensation remains, death is like a dreamless

sleep. ■ Death is like a dreamless sleep. ■ Anyone will consider a dreamless sleep better than

most days and nights. ■ Anyone will consider death better than most days

and nights. ■ Anything that is better than most days and nights is

a blessing. ■ --- ■ Death is a blessing.

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Example

■ Death is to be deprived of all sensation. (Assumption) ■ If no sensation remains, death is like a dreamless sleep.

(Assumption) ■ Death is like a dreamless sleep. (Conclusion from 1 and 2) ■ Anyone will consider a dreamless sleep better than most days

and nights. (Assumption) ■ Anyone will consider death better than most days and nights.

(Conclusion from 3 and 4) ■ Anything that is better than most days and nights is a blessing.

(Assumption) ■ --- ■ Death is a blessing. (From 3, 5, and 6)

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Deductive or Inductive?

▪ I heard lots of barking last night. The neighbor’s dog must’ve been pretty upset about something, since he rarely barks.

InductiveThe speaker is relying on a collection of experiences to draw an inference. The speaker infers that the barking emanates from a dog, and not just any dog but the neighbor’s dog. Moreover, the speaker associates being upset with lots of barking, and a lack of the latter with respect to the neighbor’s dog.

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Deductive or Inductive?

▪ All dogs bark. Fido is a dog, so he barks.

DeductiveThe premises guarantee the conclusion.

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Deductive or Inductive?

▪ On a National Geographic map, no two adjacent nations appear shaded with the same color. Brazil is shaded green on this map, and it is a National Geographic map. Only two nations in South America are not adjacent to Brazil. So at most three South American nations on this map are shaded green.

DeductiveThe conclusion follows necessarily from the premises, so this is a deductive argument.

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Deductive or Inductive?

▪ The majority rules in the House of Representatives. Either the Democrats or the Republicans will control the House of Representatives. As there are an odd number of representatives in the House, it follows that there is no way there will be a tie in the House of Representatives.

DeductiveThis conclusion follows necessarily from the premises, so it is deductive.

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Deductive or Inductive?

▪ No book in English begins numbering its pages on a left-hand page. This is a book in English, therefore it will begin its numbering on a right-hand page.

DeductiveThe conclusion follows necessarily from the premises, so this is a deductive argument.

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Deductive or Inductive?

▪ Based on a survey of 2200 randomly selected likely voters, 56.2% indicate that they will vote for the incumbent in the upcoming election. Therefore, approximately 56% of the votes in the upcoming election will be for the incumbent.

InductiveThe conclusion does not follow necessarily from the premise. The conclusion follows with some probability, if the generalization was done well.

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Deductive or Inductive?

▪ The overwhelming majority of mutations are not beneficial to an organism’s survival. So the odds are that no mutation is going to give an organism super powers.

InductiveAs words such as “majority” and “odds” indicate, this is an inductive argument.

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Deductive or Inductive?

▪ Some cookies are burnt. Some burnt things are good to eat. So some cookies are good to eat.

InductiveThe conclusion does not follow necessarily from the premises, as the some cookies in the first premise may not be any part of the some burnt things in the second premise. At best the conclusion may be probable, so this argument is best classified as inductive.

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Deductive or Inductive?

▪ The telegraph was a technological breakthrough that allowed rapid communication across vast distances. In doing so, it made communities more homogeneous and diminished diversity. Ultimately, the benefits probably outweigh such hard-to-measure costs.

InductiveThe conclusion is claimed to follow with probability, so it is inductive.

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Deductive or Inductive?

▪ All reptiles ever examined are cold-blooded. Dinosaurs resemble reptiles in many ways. So dinosaurs were cold-blooded.

InductiveNot every argument with the word “all” in it is deductive. This argument settles for probability twice, by allowing that all reptiles that have been examined are cold-blooded, and that dinosaurs resemble reptiles.