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An Introduction to Arguments

Deduction and Induction

 definition  An argument is a set of statements, one of

which is understood to be the conclusion, and the others of which are understood to be premises, with the premises being offered as supporting, or providing reasons for, the conclusion.

 Every argument has at least one premise, but there is no limit to how many it can have. Every argument has exactly one conclusion.

 DOPH 1.2 pg 28, PreClass Reading (Online)

Arguments

 An example of an argument:  (P1:) To discriminate against someone

because of his or her handicap is wrong.  (P2:) What Robert Latimer did was to

discriminate against someone—his daughter—because of her handicap.

 (C:) What Robert Latimer did was wrong.

Arguments

 Let’s try this ourselves…  Pick one or two arguments from the

“Identifying Arguments HO” pdf attached to this week’s module and try to identify and distinguish between the premises and the conclusion.

Arguments

 Validity  A valid argument is one whose conclusion

cannot be false if its premises are true. That is, it is one whose premises imply, or entail, its conclusion. We often say that it is one whose conclusion “follows from” its premises.

Deductive Arguments

 an example of a valid argument  See the example of an argument, above. That’s a

valid argument.

 (P1:) Everything in the ocean is alive.  (P2:) Jellyfish are in the ocean.  (C:) So, Jellyfish are alive.

Deductive Arguments

 Kinds of (valid) Deductive Arguments!!!  Let’s check out DOPH 1.2, pg 31  Important note: All deductive arguments are attempting to be

valid and, thus, all the basic forms/kinds are valid. However, just because an argument is invalid does not mean that it is not deductive. Sometimes we just fail emulating the valid forms/kinds and commit an informal fallacy (an invalid argument that is not inductive. Yes, all inductive arguments are invalid, more on this later).

Deductive Arguments

 An example of an invalid argument

 (P1:) People don’t like what Robert Latimer did.

 (C:) What Robert Latimer did was wrong.

 Ex2

 (P1:) All humans are mammals.

 (P2:) All whales are mammals.

 (C:) So, all humans are Whales.

Deductive Arguments

Deductive Arguments

 Validity and the truth of the premises:  (P1:) All eight-legged creatures have wings.  (P2:) A spider is an eight-legged creature.  (C:) Therefore spiders have wings.

 Valid but one of the premises is false.

Deductive Arguments

 A valid argument…

 May have a true conclusion or a false one;

 Likewise, its premises may all be true, or some of them may be true, or none of them may be true. The same goes for invalid arguments.

 So, remember, it all boils down to form-so you must ask yourself the question: IF the premises are true, MUST the conclusion be true.

Deductive Arguments

 Soundness  A sound argument is a valid one whose

premises are true.

 (P1:) All Dogs are mammals.

 (P2:) Martha is a dog.

 (C:) So, Martha is a Mammal.

Deductive Arguments

 Example of an unsound argument:

 (P1:) All Dogs are reptiles.

 (P2:) Martha is a dog.

 (C:) So, Martha is a reptile

Deductive Arguments

 Valid or invalid? if valid, sound or unsound?  first argument

 (P1:) Miami was founded in 1922.  (P2:) If Miami was founded in 1922, then it is less than

100 years old.

 (C:) Miami is less than 100 years old.

 second argument  (P1:) Either Florida in the U.S. or France is.

 (P2:) France is not in the U.S.  (C:) Florida is in the U.S.

Deductive Arguments

 third argument  (P1:) Denver is in Colorado.

 (P2:) Las Vegas is in Nevada.

 (C:) Denver is in Colorado and Las Vegas is in

Nevada and Los Angeles is in California.

 Fourth argument  (P1:) All whales are mammals.

 (P2:) All mammals are warm-blooded.

 (C:) So all whales are warm-blooded

Deductive Arguments

 5th Argument  (p1)All students eat pizza.  (p2) Jimmy is a student at FIU.  (C) Therefore, Jimmy eats pizza.

 6th Argument  (p1)All athletes work out in the gym.  (p2) Barry Bonds is an athlete.  (c) Therefore, Barry Bonds works out in the

gym.

Deductive Arguments

 7th Argument  (P1) If Joe has acute appendicitis, he is very

sick.  (P2) But Joe is very sick.  (C) Therefore Joe has acute appendicitis.

 8th Argument  (p1)All athletes work out in the gym.  (p2) Barry Bonds is an athlete.  (c) Therefore, Barry Bonds works out in the

gym.

Deductive Arguments

 Inductive arguments do not try to establish their conclusions with certainty. Instead, an inductive argument claims that its premises make the conclusion probable. Inductive arguments cannot be valid or invalid. Instead, they are weak or strong, better or worse. And even when the premises are true and provide very strong support for the conclusion, the conclusion cannot be certain. The strongest inductive argument is not as conclusive as a sound deductive argument.

Inductive arguments

 Here is a simple example:

 (P1) Most corporate lawyers are conservatives.

 (P2) Betty Morse is a corporate lawyer.

 (C) Therefore Betty Morse is a conservative.

 This is a pretty good inductive argument, because (let us say) both premises are true. Thus, the conclusion is more likely true than false.

 Inductive arguments and their cogency can be put in terms of how likely you are to bet on the conclusion given the premises given in support of the claim.

Inductive Arguments

 But now, let’s say we learn something new:

 (P3) Betty Morse is an officer of the American Civil Liberties Union.

 And we already know that:

 (P4) Most officers of the American Civil Liberties Union are not conservatives.

 Now our inductive argument has been greatly weakened, and it no longer seems probable that Betty Morse is a conservative.

 I’m definitely less likely to bet on this conclusion now.

Inductive Arguments

Kinds of Inductive Arguments!  DOPH pg 34

Inductive Arguments

 Inductive Example 2  (P1:) Every time I checked my email this week it

worked.

 (C:) My email will work today.

 Ex 3

 (P1) Socrates was Greek.

 (P2) Most Greeks eat fish.

 (C) Socrates ate fish.

Inductive Arguments

 EX 4  (P1) Two-thirds of my latino neighbors are illegal

immigrants.  (C) Therefore, two-thirds of latino immigrants come

illegally.

 EX 5

 (P1) No baby in the past has ever been able to understand quantum physics.

 (P2): Ellie is going to have a baby soon.

 (C) So Ellie’s baby is not going to be able to understand quantum physics

Inductive Argument

 EX 5

 (P1) My dad has curly hair

 (P2): My brother has curly hair

 (C) Therefore everyone I am related to has curly hair

 EX 6  (P1) Jimmy got bitten by a dog.  (P2) Most people that have been bitten by dogs become

scared of them.  (C) So, Jimmy is now scared of all dogs.

Inductive Argument