PHL145H5 Lecture 4: PHL145 - WEEK 4
Document Summary
We have said that good (deductive) arguments are such that their premises imply their conclusions. And we understood this in terms of validity: An argument p1 . pn / c is valid iff (if and only if) it is impossible that: p1 . pn are all true and c is false. Whether or not if the premise were true, the conclusion were to be true arguments valid. Premise true, and conclusion true invalid argument. What if it"s impossible to make the premise true, p not p therefore q, its valid. Its impossible to make the premises true and the argument false. Strictly speaking, validity is a semantic notion, not a syntactic notion. But validity makes reference to truth. whether or not a sentence is true is of course a semantic matter (since you have to know what a sentence means to know whether what is says is true or false) Connectives are the key ingredient to any propositional logic.
