substitutivity การใช้

Bertrand Russell thought that this demonstrated the failure of substitutivity of identicals in intensional contexts.
Saul Kripke holds that this failure may be the result of the use of the disquotational principle implicit in these proofs, and not a failure of substitutivity as such.
The second is an application of the principle of substitutivity : if a = b, then a has all the properties b has, thus from Fa, infer Fb, where F is'nec ( a =-- ) '.
Willard Van Orman Quine thought that the failure of substitutivity in intensional contexts ( e . g ., " Sally believes that " p " " or " It is necessarily the case that " q " " ) shows that modal logic is an impossible project.
Many other propositions have also been mentioned as laws of thought, including the dictum de omni et nullo attributed to Aristotle, the substitutivity of identicals ( or equals ) attributed to Euclid, the so-called identity of indiscernibles attributed to Gottfried Wilhelm Leibniz, and other " logical truths ".