Non-classical logics (and sometimes alternative logics) is the name given to formal systems that differ in a significant way from standard logical systems such as propositional and predicate logic. There are several ways in which this is done, including by way of extensions, deviations, and variations. The aim of these departures is to make it possible to construct different models of logical consequence and logical truth.

Philosophical logic, especially in theoretical computer science, is understood to encompass and focus on non-classical logics, although the term has other meanings as well.

Examples of non-classical logics

There are many kinds of non-classical logic, which include: