THE mortality of Socrates is so often asserted in books on logic that it may be as well briefly to consider what it means. The phrase " Socrates is mortal " may be thus defined : " There is at least one instant t such that t has not to Socrates the one-many relation R which is the converse of the relation ' exists a t / and all instants following t have not the relation R to Socrates, and there is at least one instant t' such that neither f nor any instant preceding t' has the relation R to Socrates."