PHIL 2100 Lecture Notes - Lecture 4: Modus Ponens, Modus Tollens, Stoicism
9 May 2016
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But what follows from what isn"t always obvious. A demonstration of how the conclusion follows is often helpful: such a demonstration is a proof or derivation . Inference rules: the inference rules capture valid forms of reasoning. Mp: modus tollens: if you have any conditional sentence along with the negation of its consequent, you may infer the negation of its antecedent. Mt: double negation: from any sentence you may infer the result of putting two negation signs on the front, or vice versa. Dn: repetition: if you have any sentence you may validly infer it from itself. R: for each of the following arguments, say whether it is an instance of mp, mt, dn, r, or none, (p q). Q p: ((p q) r). (p q) r, (p q) (p q, ( p q). q p, (p q) ( p q)
