Page:Ferrier's Works Volume 1 - Institutes of Metaphysic (1875 ed.).djvu/49

Rh equally possible. But nature could not have fixed that two straight lines should, in any circumstances, enclose a space; for this involves a contradiction.

§ 28. The logical "law of identity or contradiction," as it is called, is the general expression and criterion of all necessary truth. This law may be best exhibited by carrying it a point higher than is usually done. The law is, that a thing must be what it is. A is A. Suppose that the denier of all necessary truth, and consequently of this proposition, were to say—"No; a thing need not be what it is;" the rejoinder is—" Then your proposition, that a thing need not be what it is, need not be what it is. It may be a statement to directly the opposite effect. Which of the statements, then, is it? Is it a proposition which affirms that a thing need not be what it is, or a proposition declaratory of the very contrary?" "It is a proposition to the former effect," says he. "But how can I know that? If a thing need not be what it is, why need your proposition (which, of course, is something) be what it is? Why may it not be a declaration that a thing is and must be what it is? Give me some guarantee that it is not the latter proposition, or I cannot possibly take it up. I cannot know what it means, for it may have two meanings." The man is speechless. He cannot give me any guarantee.