Now it is also the case that there can be nothing intermediate to an assertion and a denial. We must either assert or deny any single predicate of any single subject. The quickest way to show this is by defining truth and falsity. Well, falsity is the assertion that that which is is not or that that which is not is and truth is the assertion that that which is is and that that which is not is not. Thus anyone who asserts anything to be or not to be is either telling the truth or telling a falsehood. On the other hand, neither that which is is said either not to be or to be nor is that which is not.
And if there were an intermediate of contradictory statements, then it would either be like grey between black and white or like the non-man-non-horse between man and horse.
Aristotle, The Metaphysics, Trans and Introduction by Hugh Lawson-Tancred, Penguin, London, 2004, 107 (Gamma 7 1011b)
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It is admitted that the law of identity expresses only a one-sided determinateness, that it contains only formal truth, a truth which is abstract, incomplete. In this correct judgement, however, it is immediately implied that truth is complete only in the unity of identity with difference, and hence consists only in this unity.
G.W.F. Hegel, Hegel’s Science of Logic, Trans., A.V. Miller, Humanities Press, New York, 1976, 414
the truth is concrete; that is, while it gives a bond and principle of unity, it also possesses an internal source of development
G.W.F. Hegel, Hegel’s Logic, Trans., William Wallace, Oxford University Press, Oxford, 1975, 19-20
For what subject matter can cognition have that is more sublime than truth itself!
G.W.F. Hegel, Hegel’s Science of Logic, Trans., A.V. Miller, Humanities Press, New York, 1976, 575
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Contemporary fideism does not at all reject science; all it rejects is the “exaggerated claims” of science, to wit, its claim to objective truth. If objective truth exists (as the materialists think), if natural science, reflecting the outer world in human “experience”, is alone capable of giving us objective truth, then all fideism is absolutely refuted. But if there is no objective truth, if truth (including scientific truth) is only an organising form of human experience, then this in itself is an admission of the fundamental premise of clericalism, the door is thrown open for it, and a place is cleared for the “organising forms” of religious experience.
V.I. Lenin, Materialism and Empirio-Criticism: Critical Comments on a Reactionary Philosophy, 1908, Progress Publishers, Moscow, 1975, 110
Dialectics—as Hegel in his time explained—contains an element of relativism, of negation, of scepticism, but is not reducible to relativism. The materialist dialectics of Marx and Engels certainly does contain relativism, but is not reducible to relativism, that is, it recognises the relativity of all our knowledge, not in the sense of denying objective truth, but in the sense that the limits of approximation of our knowledge to this truth are historically conditional.
V.I. Lenin, Materialism and Empirio-Criticism: Critical Comments on a Reactionary Philosophy, 1908, Progress Publishers, Moscow, 1975, 121
The standpoint of life, of practice, should be first and fundamental in the theory of knowledge. And it inevitably leads to materialism, sweeping aside the endless fabrications of professorial scholasticism. Of course, we must not forget that the criterion of practice can never, in the nature of things, either confirm or refute any human idea completely. This criterion too is sufficiently “indefinite” not to allow human knowledge to become “absolute”, but at the same time it is sufficiently definite to wage a ruthless fight on all varieties of idealism and agnosticism. If what our practice confirms is the sole, ultimate and objective truth, then from this must follow the recognition that the only path to this truth is the path of science, which holds the materialist point of view.
V.I. Lenin, Materialism and Empirio-Criticism: Critical Comments on a Reactionary Philosophy, 1908, Progress Publishers, Moscow, 1975, 126-27