''A posteriori'' necessity is a thesis in

metaphysics Metaphysics is the branch of philosophy that examines the basic structure of reality. It is traditionally seen as the study of mind-independent features of the world, but some theorists view it as an inquiry into the conceptual framework of ...

and the

philosophy of language Philosophy of language refers to the philosophical study of the nature of language. It investigates the relationship between language, language users, and the world. Investigations may include inquiry into the nature of Meaning (philosophy), me ...

, that some statements of which we must acquire knowledge ''

a posteriori ('from the earlier') and ('from the later') are Latin phrases used in philosophy to distinguish types of knowledge, justification, or argument by their reliance on experience. knowledge is independent from any experience. Examples include ...

'' are also necessarily true. It challenges previously widespread belief that only ''

a priori ('from the earlier') and ('from the later') are Latin phrases used in philosophy to distinguish types of knowledge, Justification (epistemology), justification, or argument by their reliance on experience. knowledge is independent from any ...

'' knowledge can be necessary. It draws on a number of philosophical concepts such as necessity, the

causal theory of reference A causal theory of reference or historical chain theory of reference is a theory of how terms acquire specific referents based on evidence. Such theories have been used to describe many referring terms, particularly logical terms, proper names, an ...

, rigidity, and the ''a priori''–''a posteriori'' distinction. It was first introduced by philosopher

Saul Kripke Saul Aaron Kripke (; November 13, 1940 – September 15, 2022) was an American analytic philosophy, analytic philosopher and logician. He was Distinguished Professor of Philosophy at the Graduate Center of the City University of New York and emer ...

in his 1970 series of lectures at

Princeton University Princeton University is a private university, private Ivy League research university in Princeton, New Jersey, United States. Founded in 1746 in Elizabeth, New Jersey, Elizabeth as the College of New Jersey, Princeton is the List of Colonial ...

. The transcript of these lectures was then compiled and assembled into his seminal book, ''

Naming and Necessity ''Naming and Necessity'' is a 1980 book with the transcript of three lectures, given by the philosopher Saul Kripke, at Princeton University in 1970, in which he dealt with the debates of proper names in the philosophy of language. The transcript ...

''.

Main argument for ''a posteriori'' necessity

Here is an overview of the argument: :(P1) 'Hesperus' is a proper name that refers to the evening star. 'Phosphorus' is also a proper name and it refers to the morning star. But the evening star and the morning star are the same planetary body (Venus). So both names designate Venus. :(P2) If both names designate rigidly, they designate the same object (Venus) in every possible world in which it exists. Therefore (by the definition of 'necessary') 'Hesperus = Phosphorus' is necessarily true. If it is the case that in all possible worlds the identity claim "Hesperus is Phosphorus" is true, the statement is necessary. :(P3) The fact that Hesperus is Phosphorus was discovered by empirical observation, and it could not have been discovered ''a priori''. Therefore, it is known ''a posteriori''. :(C) Therefore, it is possible for knowledge obtained ''a posteriori'' to be necessary. Other instances of ''a posteriori'' necessary truths include: " is water".

Significance

''Naming and Necessity'' is among the most important philosophical works of the 20th century. ''A posteriori'' necessity existing would make the distinction between a prioricity, analyticity, and necessity harder to discern because they were previously thought to be largely separated from the ''a posteriori'', the synthetic, and the contingent. (a) ''P'' is ''a priori''

iff In logic and related fields such as mathematics and philosophy, "if and only if" (often shortened as "iff") is paraphrased by the biconditional, a logical connective between statements. The biconditional is true in two cases, where either both ...

''P'' is necessary. (b) ''P'' is ''a posteriori'' iff ''P'' is contingent.

Hilary Putnam Hilary Whitehall Putnam (; July 31, 1926 – March 13, 2016) was an American philosopher, mathematician, computer scientist, and figure in analytic philosophy in the second half of the 20th century. He contributed to the studies of philosophy of ...

comments on the significance of Kripke's counter-examples: "Since Kant there has been a big split between philosophers who thought that all necessary truths were analytic and philosophers who thought that some necessary truths were synthetic ''a priori''. But none of these philosophers thought that a (metaphysically) necessary truth could fail to be ''a priori''."

References

{{Use dmy dates, date=May 2024 Necessity

necessity Necessary or necessity may refer to: Concept of necessity * Need ** An action somebody may feel they must do ** An important task or essential thing to do at a particular time or by a particular moment * Necessary and sufficient condition, in l ...

Concepts in epistemology Concepts in the philosophy of language Concepts in metaphysics

Main argument for ''a posteriori'' necessity

Significance

See also

References