PHIL 10 Lecture 9: Chapter 4
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Phil 10 lecture 9 chapter 4. Examples: (~m v p) (k ~l, ~k v l, -> ~m, ~m v p, k ~l, k, ~l, ~k, ----k ~k, m, m v k. Rules for the use of ip (indirect proof) Start subproof (sp) by indenting and naming first line aip. Mark off ip, close sp, discharging assumption. Next line can only be negation of aip. Examples: c (a d, b (a e, -> c b, c, a d, a, --(c b) a, ~ (c b) v a. / ~ (c b) v a. If a statement can be derived from no premises, we know that the statement follows from anything, will follow from any set of premises. Any argument that has statement as conclusion is valid. If this is true, that statement is tautology: no statement of any other category can have this ability. Examples: ->~p, ~p v ~p, ----p ~p, ~p (p ~p)