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Logic: The Language of Philosophy. What is Logic? Logic is the study of argumentation o In Philosophy, there are no right or wrong opinions, but there.

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Presentation on theme: "Logic: The Language of Philosophy. What is Logic? Logic is the study of argumentation o In Philosophy, there are no right or wrong opinions, but there."— Presentation transcript:

1 Logic: The Language of Philosophy

2 What is Logic? Logic is the study of argumentation o In Philosophy, there are no right or wrong opinions, but there are arguments that are better than others.

3 What is an “Argument”? Argument : a set of statements consisting of at least two premises and at least one conclusion. o Premises: reasons supporting the conclusion o Conclusion: the statement you are trying to prove

4 Philosophers write arguments like this: 1.Socrates is a man.(premises) 2.All men are mortal --------------------------- 3. Socrates is mortal(conclusion)

5 Arguments must be valid and sound An argument is valid when the premises guarantee the conclusion o This is not subjective An argument is sound if (1) it is valid; and (2) the premises are true

6 Argument Forms I. Modus Ponens ( “ Affirming Mode ” ) P→Q1. If the ground is wet, then it was raining. P2. The ground is wet. ------------------------------------------------------------- Q3. Therefore, it was raining.

7 Modus Tollens Modus Tollens Latin for “ Denying Mode ” P→Q1. If the ground is wet, then it was raining. ~Q2. It was not raining ------------------------------------------------------------ ~P3. Therefore, the ground is not wet.

8 Common Errors P→Q ~P Q -------- --------- ~Q P Denying the Antecedent Affirming the Consequent

9 Denying the Antecedent P→Q 1. If Socrates is French, then Socrates is mortal ~P 2. Socrates is not French -------- ------------------------------------------------------------------ ~Q 3. Socrates is not mortal NOT VALID!

10 Affirming the Consequent P→Q 1. If Socrates is French, then Socrates is mortal. Q 2. Socrates is mortal. -------- -------------------------------------------------------------------- P 3. Socrates is French NOT VALID!

11 Chain Reasoning P  Q1. Nellie is a dog. Q  R 2. A dog is a mammal. ------------------------------------- P  R3. Nellie is a mammal.

12 Disjunctive Syllogism P  Q1. Either the maid did it or the butler did it. ~P2. The maid did not do it. -------------------------------------------------------------- Q3. Therefore, the butler did it.

13 Hypothetical Syllogism P→Q1. If Jim comes to the party, then Chris will come too. Q→R2. If Chris comes to the party, then Pat will come too. -------------------------------------------------------------------- P→R3. Therefore, if Jim comes to the party, Pat will come too.

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