Existential instantiation

In predicate logic, existential instantiation (also called existential elimination)[1][2][3] is a valid rule of inference which says that, given a formula of the form , one may infer for a new constant symbol c. The rule has the restriction that the constant c introduced by the rule must be a new term that has not occurred earlier in the proof.

In one formal notation, the rule may be denoted by

where a is a new constant symbol that has not appeared in the proof.

See also


  1. Hurley, Patrick. A Concise Introduction to Logic. Wadsworth Pub Co, 2008.
  2. Copi and Cohen
  3. Moore and Parker
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