substitutivity en · NOUN
Etymology
Etymology tree English substitutive Proto-Indo-European *-teh₂ Proto-Indo-European *-ts Proto-Indo-European *-teh₂ts Latin -itāsder. Old French -itebor. Middle English -ite English -ity English substitutivity From substitutive + -ity.
Meanings
-
(uncountable) A logical relationship in which two terms can be mutually substituted without affecting the truth value of any propositions in which the terms occur, thereby establishing that the terms are identical.
One of the fundamental principles governing identity is that of substitutivity—or, as it might well be called, that of indiscernibility of identicals. It provides that, given a true statement of identity, one of its two terms may be substituted for the other in any true statement and the result will be true.
1943, Willard V. Quine, “Notes on Existence and Necessity”, in The Journal of Philosophy, volume 40, number 5, page 113: