Thursday, July 13 2000
An argument is sound, if it is valid and its premises are true. (Handout #5).
An argument is formal if the validity of the argument does not depend on the meaning of the symbols employed. (Handout #5).
From the assumption A and the derivation of a contradiction you
infer `not A'. (Lecture 7/12/00)
From the assumption A and the derivation of a contradiction you infer `not A'. (Lecture 7/12/00)
Assume: God does not exist.
Then, there is something more perfect than God, by assumption (b).
In other words, God is not the most perfect being.
This contradicts the assumption (a).
Therefore, by reductio ad absurdum, God does exist. (This argument is attributed to Descartes.)
The argument is not valid. Because it is possible for the premises to be true, but the conclusion to be false, for example, if my income rises because of a raise and not because of the lowering of my taxes. (Lecture 7/11/00)