1.4 Validity, Truth, Soundness, Strength and Cogency

Learn the terms used to evaluate inductive and deductive arguments

Deductive Arguments❖ An argument in which it is claimed that it is impossible

for the conclusion to be false if the premises are true is a deductive argument.

❖ That is, it is claimed that the argument it valid.

❖ In a valid argument, if the premises are true, the conclusion must be true too.

❖ “Validity” describes the relationship that the premises bear to the conclusion in a deductive argument.

❖ The test for validity: Imagine that the premises are true and the conclusion is false

❖ If you cannot imagine that the premises are true and the conclusion is false, then the argument is VALID.

❖ If you can imagine that the premises are true and the conclusion is false then the argument is INVALID.

❖ P1. All CCU students are hardworking. P2. Howie is a CCU student.

❖ C. So, Howie is hardworking.

❖ Valid: if the premises were true, the conclusion could not be false.

❖ P1. All CCU students are hardworking. P2. Howie is hardworking.

❖ C. So, Howie is a CCU student.

❖ Invalid: if the premises were true, the conclusion could still be false.

❖ In a “good” argument the premises support the conclusion (validity) AND the premises are true.

❖ A “good” deductive argument is called a “sound” argument. A sound argument is valid and has all true premises.

❖ P1. All CCU students are hardworking. P2. Howie is a CCU student.

❖ C. So, Howie is hardworking.

❖ Valid: if the premises were true, the conclusion could not be false.

❖ False premise(s) Unsound

Sound = Valid + True Premises

❖ P1. If Obama is president then he is Commander in Chief.

❖ P2. Obama is president.

❖ C. Therefore, he is Commander in Chief.

❖ Is this argument sound?

Sound = Valid + True Premises

❖ P1. All cats have tails.

❖ P2. My dog has a tail.

❖ C. So, my dog is a cat.

❖ Is this argument sound?

Inductive Arguments❖ An argument in which it is claimed that it is improbably

that the conclusion is false if the premises are true is an inductive argument.

❖ That is, it is claimed that the argument is strong.

❖ A strong argument is one whose conclusion is probably true given the truth of the premises.

❖ The test for strength: Imagine the premises are true, and determine whether the conclusion is probable given the truth of the premises.

❖ Does the truth of the premises make it more like that the conclusion is true then had the premises been false?

❖ P1. All past presidents have been men.

❖ C. The next president will be a man.

❖ Inductive: It is possible for the conclusion to be false

❖ Can be made stronger or weaker given more information.

❖ There are degrees of strength!

❖ P1. All past presidents have been men.

❖ C. The next president will be a man.

❖ P1. All past presidents have been women.

❖ C. The next president will be a woman.

❖ Arguments = Premises + conclusions

❖ Factual claim (are the premises true?)

❖ Inferential claim (is the argument valid/strong?)

❖ Deductive Arguments:

❖ Sound = Valid + True premises

❖ {valid: if the premises are true, the conclusion must be true}

❖ Inductive Arguments

❖ Cogent = Strong + True Premises

❖ {strong: the conclusion is probably true if the premises are true}