# Category: Classical logic

Principle of explosion
In classical logic, intuitionistic logic and similar logical systems, the principle of explosion (Latin: ex falso [sequitur] quodlibet, 'from falsehood, anything [follows]'; or ex contradictione [sequ
Begriffsschrift
Begriffsschrift (German for, roughly, "concept-script") is a book on logic by Gottlob Frege, published in 1879, and the formal system set out in that book. Begriffsschrift is usually translated as con
Ludwig Wittgenstein
Ludwig Josef Johann Wittgenstein (/ˈvɪtɡənʃtaɪn, -staɪn/ VIT-gən-s(h)tyne; German: [ˈluːtvɪç ˈjoːzɛf 'joːhan ˈvɪtɡn̩ʃtaɪn]; 26 April 1889 – 29 April 1951) was an Austrian-British philosopher who worke
Propositional calculus
Propositional calculus is a branch of logic. It is also called propositional logic, statement logic, sentential calculus, sentential logic, or sometimes zeroth-order logic. It deals with propositions
Disjunctive syllogism
In classical logic, disjunctive syllogism (historically known as modus tollendo ponens (MTP), Latin for "mode that affirms by denying") is a valid argument form which is a syllogism having a disjuncti
Commutativity of conjunction
In propositional logic, the commutativity of conjunction is a valid argument form and truth-functional tautology. It is considered to be a law of classical logic. It is the principle that the conjunct
Modus tollens
In propositional logic, modus tollens (/ˈmoʊdəs ˈtɒlɛnz/) (MT), also known as modus tollendo tollens (Latin for "method of removing by taking away") and denying the consequent, is a deductive argument
Import–export (logic)
In logic, import-export is a deductive argument form which states that . In natural language terms, the principle means that the following English sentences are logically equivalent. 1. * If Mary isn
Law of thought
The laws of thought are fundamental axiomatic rules upon which rational discourse itself is often considered to be based. The formulation and clarification of such rules have a long tradition in the h
Problem of multiple generality
The problem of multiple generality names a failure in traditional logic to describe certain intuitively valid inferences. For example, it is intuitively clear that if: Some cat is feared by every mous