Kripke semanticsKripke semantics (also known as relational semantics or frame semantics, and often confused with possible world semantics) is a formal semantics for non-classical logic systems created in the late 1950s and early 1960s by Saul Kripke and André Joyal. It was first conceived for modal logics, and later adapted to intuitionistic logic and other non-classical systems. The development of Kripke semantics was a breakthrough in the theory of non-classical logics, because the model theory of such logics was almost non-existent before Kripke (algebraic semantics existed, but were considered 'syntax in disguise').
Modal logicModal logic is a kind of logic used to represent statements about necessity and possibility. It plays a major role in philosophy and related fields as a tool for understanding concepts such as knowledge, obligation, and causation. For instance, in epistemic modal logic, the formula can be used to represent the statement that is known. In deontic modal logic, that same formula can represent that is a moral obligation. Modal logic considers the inferences that modal statements give rise to.
Western philosophyWestern philosophy encompasses the philosophical thought and work of the Western world. Historically, the term refers to the philosophical thinking of Western culture, beginning with the ancient Greek philosophy of the pre-Socratics. The word philosophy itself originated from the Ancient Greek (φιλοσοφία), literally, "the love of wisdom" φιλεῖν , "to love" and σοφία sophía, "wisdom").
Philosophical logicUnderstood in a narrow sense, philosophical logic is the area of logic that studies the application of logical methods to philosophical problems, often in the form of extended logical systems like modal logic. Some theorists conceive philosophical logic in a wider sense as the study of the scope and nature of logic in general. In this sense, philosophical logic can be seen as identical to the philosophy of logic, which includes additional topics like how to define logic or a discussion of the fundamental concepts of logic.
A priori and a posterioriA priori ("from the earlier") and a posteriori ("from the later") are Latin phrases used in philosophy to distinguish types of knowledge, justification, or argument by their reliance on experience. A priori knowledge is independent from any experience. Examples include mathematics, tautologies, and deduction from pure reason. A posteriori knowledge depends on empirical evidence. Examples include most fields of science and aspects of personal knowledge. The terms originate from the analytic methods found in Organon, a collection of works by Aristotle.
IndexicalityIn semiotics, linguistics, anthropology, and philosophy of language, indexicality is the phenomenon of a sign pointing to (or indexing) some element in the context in which it occurs. A sign that signifies indexically is called an index or, in philosophy, an indexical. The modern concept originates in the semiotic theory of Charles Sanders Peirce, in which indexicality is one of the three fundamental sign modalities by which a sign relates to its referent (the others being iconicity and symbolism).
On the Plurality of WorldsOn the Plurality of Worlds (1986) is a book by the philosopher David Lewis that defends the thesis of modal realism. "The thesis states that the world we are part of is but one of a plurality of worlds," as he writes in the preface, "and that we who inhabit this world are only a few out of all the inhabitants of all the worlds." It is not to be confused with cosmic pluralism. The book is divided into four chapters. Chapter 1 begins with an exposition of modal realism.
Accessibility relationAn accessibility relation is a relation which plays a key role in assigning truth values to sentences in the relational semantics for modal logic. In relational semantics, a modal formula's truth value at a possible world can depend on what's true at another possible world , but only if the accessibility relation relates to . For instance, if holds at some world such that , the formula will be true at . The fact is crucial. If did not relate to , then would be false at unless also held at some other world such that .
Impossible worldIn philosophical logic, the concept of an impossible world (sometimes called a non-normal world) is used to model certain phenomena that cannot be adequately handled using ordinary possible worlds. An impossible world, , is the same sort of thing as a possible world (whatever that may be), except that it is in some sense "impossible." Depending on the context, this may mean that some contradictions, statements of the form are true at , or that the normal laws of logic, metaphysics, and mathematics, fail to hold at , or both.
Philosophical zombieA philosophical zombie (or "p-zombie") is a being in a thought experiment in philosophy of mind that is physically identical to a normal person but does not have conscious experience. For example, if a philosophical zombie were poked with a sharp object, it would not feel any pain, but it would behave exactly the way any conscious human would. Philosophical zombie arguments are used against forms of physicalism and in defense of the "hard problem of consciousness", which is the problem of accounting in physical terms for subjective, intrinsic, first-person, what-it's-like-ness experiences.
