INTRODUCTION.
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equally possible. But nature could not have fixed that two straight lines should, in any circumstances, enclose a space; for this involves a contradiction.
Its criterion is "the law of contradiction." Law explained.§ 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.