; it is true when our original statement is true, and it is formally equivalent to the original function of
if this original function is extensional; but when the original function is intensional, the new one is more often true than the old one. For example, consider again "I believe that all men are mortal," regarded as a function of "
is human." The derived extensional function is: "There is a function formally equivalent to '
is human' and such that I believe that whatever satisfies it is mortal." This remains true when we substitute "
is a rational animal" for "