COMP 232 Lecture Notes - Lecture 5: Modus Ponens, I Feel Sick, Modus Tollens

• School: Concordia University
• Department: Computer Sci.
• Course: COMP 232
• Professor: Gosta Grahne

Document Summary

Here p, q, and r are called premises and s is called the conclusion. An argument is called valid if the truth of the conclusion follows necessarily (by logical form alone) from the truth of its premises. When an argument is valid, and the premises are true, then the conclusion must be true. This has the argument form: p q p. Note that when the premises are both true, the conclusion is also true. The following argument form is invalid: p q q p. Truth table: premise premise conclusion p q q p p q. In the last row, both premises are true, but the conclusion is false. They give a justi cation for obtaining a con- clusion from facts that are known or can be assumed. B is the tautology a b t rue. read as. If a is true, then we conclude that b is true. P q p p q. P p q q r.