Classical logic

branch of logic concerned with the study of propositions (whether they are true or false) that are formed by other propositions with the use of logical connectives, and how their value depends on the truth value of their components

logical formula which is true in every possible interpretation

logical principle stating that for every proposition, either it or its negation is true

theorem of logic

if X implies Y, and X is true, then Y is true

if X implies Y, and Y isn't true, then neither is X

class of formal logics

Begriffsschrift (German for, roughly, "concept-writing") is a book on logic by Gottlob Frege, published in 1879, and the formal system set out in that book.

theorem which states that any statement can be proven from a contradiction

term

inference rule in logics : with "A or B" and "not A" deduce "B"

theorem

failure in traditional logic to describe certain intuitively valid inferences