E. V. Ilyenkov 1979
Source: The problem of contradiction in logic, in B. M. Kedrov, Dialekticheskoe protovorichie [Dialectical Contradiction], Moscow: Politizdat, 1979, pp. 122-143.
The logic which we discuss is not at all concerned with specific forms of the expression of thought in language in general, and still less with an artificial “language of science,” but with the forms of thought itself, understood as a “scientific-historical process” (K. Marx), which is by no means realized only in language.
Obviously the forms of thought are expressed (and realized) in language, in forms of language, but the main difference between this error and others which would be worse, but are also especially unpardonable for specialists in logic, is overlooked. It is impossible to put the identity sign between forms of thought and forms of expression of thought unless we put both feet on the ground of the old philosophical prejudice according to which language in general (in the broadest sense) is the one “external form” in which thought is realized, “manifested,” “becomes explicit,” and hence thought is also investigated. In that case, indeed, forms and norms of “language” would be also uniquely accessible to observation and investigation of the “forms of thought,” its logical norms. However, this prejudice, as given and well-known, is fraught with sad consequences for the science of thought, in particular, a threat of the complete degeneration of logic as a science investigating general and necessary forms and laws of thought, into purely subjective “rules,” not having and not being able to have any objective basis and justification except that they are established by an amicable agreement (“conventionally”); “logic” in such an interpretation is unavoidably transformed into something resembling that convention which was previously violated by Panikovskii. Identifying the forms of thought with forms of language, by means of the [identity] sign whose logic was worked out by the Stoics and the Medieval scholastics, had, finally, its historical justification, which has disappeared into oblivion....
If logical forms are found not only in acts of speaking of the surrounding world, but also in acts of really changing it in human practice, then practice proves to be the criterion of “justification” of logical figures directing human speech, man’s verbally formalized self-consciousness. Logical forms (schemes, figures) are the forms within whose framework human activity in general is performed, to whatever particular object it may be directed, but it words, things, or events, historical situations.  And if we find some figure only in the verbal form of the passage of thought, and cannot find it in the real affairs of men (as their abstract scheme), then this means that we are not confronted with any kind of logical form, but only with forms of speech. Practice also remains the criterion for logic, the determining factor, and we are concerned with logical form or with nothing.
Naturally, the understanding of logic as the science of thought, as the science of activity which is realized not only in words, not only in speaking and written records of this speaking, but also (and above all!) in works, in acts of changing the external world, in experiments with fully real things, in the precess of creation of objects of labor and in changing the relations between people, the matter begins to look essentially different from the views of those who side with the old, pure formal logic. They are primarily concerned not mainly with thought, but with the mode of connection of “subject and predicate,” with the constitution of the verbal “definitions” of things, with “conjunctions of propositions,” which mutually cancel each other, and with similar situations of a linguistic rather than logical character.
From the point of view [of the science of thought rather than its expression in language] it is precisely contradiction, and not the absence of contradiction, which turns out to be the real logical form, within whose framework lies real thought, realizing itself in the aspect of the development of science, technology, and “morality.”
For just this reason Hegel was also right to make his paradoxical assertion that “Contradiction is the criterion of truth, absence of  contradiction is the criterion of error” ( Hegel, Raboty pasnykh let [Works from Various Years], t. 1., Moscow, 1970, p. 265.) Hence he was also right to deprive the notorious principle of the “exclusion of contradiction” of the status of a law of thought, the status of an absolute and undisputed “norm of truth.” ...