The purpose of this paper is to show that in the Sophist Plato develops a dialectical strategy that appeals to necessary conditions of language as a fundamental step toward establishing some principles of his ontology. This strategy constitutes a clear antecedent of the elenctic refutation offered by Aristotle in Metaphysics Gamma 4 against the denier of the principle of non-contradiction and could be described as transcendental because it refers to conditions without which there wouldn’t be any speech. The paper aims (...) to show that such a strategy is used both by Plato and Aristotle to deal with radical adversaries whose refutation allows the establishment of basic theses of their own philosophies. (shrink)