PHI 1101 Lecture Notes - Lecture 6: Deductive Reasoning, Modus Tollens, Modus Ponens

• School: University of Ottawa
• Department: Philosophy
• Course: PHI 1101
• Professor: Sardar Hosseini

Document Summary

**note-prof said we (cid:449)ill (cid:374)ot (cid:272)o(cid:448)e(cid:396) the (cid:373)ate(cid:396)ial i(cid:374) the se(cid:272)tio(cid:374) e(cid:374)titled (cid:862)equivalent forms(cid:863), pp. (cid:1010)(cid:1008)-75. Common deductive argument types (1) argument based on mathematics: Example: mark has twice as many cats as susan. Susan has 3 cats; therefore, mark has 6 cats. (2) argument from definition: truth of conclusion is guaranteed by definition. O(cid:396), ja(cid:272)kso(cid:374) is a lia(cid:396); the(cid:396)efo(cid:396)e, he does(cid:374)(cid:859)t tell the t(cid:396)uth. (3) categorical syllogism: syllogism (two premised argument) with each statement starting (cid:449)ith (cid:862)all,(cid:863) (cid:862)so(cid:373)e,(cid:863) (cid:862)(cid:374)o(cid:374)e,(cid:863) o(cid:396) (cid:862)e(cid:448)e(cid:396)y. (cid:863) (cid:894)(cid:272)hapte(cid:396) (cid:1009)(cid:895) Therefore, socrates is mortal. (4) sentential (propositional) deductive arguments: An argument intended to provide logically conclusive support for its conclusion. The defining characteristic of a deductive argument is that it is valid or invalid. Examples: if a dog bites the mailman, it (cid:373)ust (cid:271)e pu(cid:374)ished. In this case, we may conceive that the conclusion does not follow inescapably from the premises.