Kitap 4
8
For the principle which the student of any form of Being must grasp is no hypothesis; and that which a man must know if he knows anything he must bring with him to his task.
8
Clearly, then, it is a principle of this kind that is the most certain of all principles. Let us next state what this principle is.
9
It is impossible for the same attribute at once to belong and not to belong to the same thing and in the same relation; and we must add any further qualifications that may be necessary to meet logical objections. This is the most certain of all principles, since it possesses the required definition;
10
for it is impossible for anyone to suppose that the same thing is and is not, as some imagine that Heraclitus saysFor examples of Heraclitus’s paradoxes cf. Heraclitus Fr. 36, 57, 59 (Bywater); and for their meaning see Burnet, E.G.P. 80.—for what a man says does not necessarily represent what he believes.
11
And if it is impossible for contrary attributes to belong at the same time to the same subject (the usual qualifications must be added to this premiss also), and an opinion which contradicts another is contrary to it, then clearly it is impossible for the same man to suppose at the same time that the same thing is and is not; for the man who made this error would entertain two contrary opinions at the same time.
12
Hence all men who are demonstrating anything refer back to this as an ultimate belief; for it is by nature the starting-point of all the other axioms as well.
1
There are some, however, as we have said, who both state themselves that the same thing can be and not be, and say that it is possible to hold this view. Many even of the physicists adopt this theory. But we have just assumed that it is impossible at once to be and not to be, and by this means we have proved that this is the most certain of all principles.
