“To say of what is that it is not, or if what is not that it is, is false, while to say of what is that it is, is false, while to say of what is that it is, and of what is not that is not, is true; so that he who says of anything that it is, or that it is not, will say either what is true or what is fase; but neither what is nor what is not is said to be or note to be.”