Supervenience

In philosophy, supervenience refers to a relation between sets of properties or sets of facts. X is said to supervene on Y if and only if some difference in Y is necessary for any difference in X to be possible.

Examples of supervenience, in which case the truth values of some propositions cannot vary unless the truth values of some other propositions vary, include:

  • Whether there is a table in the living room supervenes on the positions of molecules in the living room.
  • The truth value of (A) supervenes on the truth value of its negation, (¬A), and vice versa.

Supervenience is of interest to philosophers because it differs from other nearby relations, for example entailment. Some philosophers believe it possible for some A to supervene on some B without being entailed by B. In such cases it may seem puzzling why A should supervene on B and equivalently why changes in A should require changes in B. Two important applications of supervenience involve cases like this. One of these is the supervenience of mental properties (like the sensation of pain) on physical properties (like the firing of 'pain neurons'). A second is the supervenience of normative facts (facts about how things ought to be) on natural facts (facts about how things are).

The possibility of "supervenience without entailment" or "supervenience without reduction" is contested territory among philosophers.

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