Did Antisthenes claim that there is no such thing as contradiction?

Antisthenes is credited with a remarkable theory: contradiction is impossible. Diogenes Laertius ascribes the tenet of the excluded contradiction expressly to Antisthenes, and it is a theory well suited to Antisthenes’ provocative attitude. It amounts to saying ‘you cannot be contradicted, you are always right’ – what a charming theory for the future politicians who were Antisthenes’ pupils! A witness for this thesis is a quotation from Proclus: ‘That it is not necessary to contradict, because every logos speaks the truth, he [sc. Antisthenes] says, for he who speaks says something, and he who says something, speaks being, and he who speaks being, speaks the truth’. ‘Being’ (τὸ ὄν) is what really is, what is true, what is valid. Thus, it turns out that Antisthenes’ ontology and gnoseology coincided: if one says ‘being’, one speaks the truth; being apparently has an actual existence experienced without metaphysics. If Antisthenes truly considered logos a kind of definition, then, for example, referring to an animal by the name of ‘horse’ labels an actual existing horse, a being; in that case something that is true is spoken, and such knowledge can spring only from reality.

Furthermore, contradiction is not necessary, he claims: it is possible that both debaters are saying something that is true and there is no need to assume that a contradiction is present. However, it is not easy to fathom precisely what Antisthenes had in mind when he launched this view. In the scholarly literature Proclus’ statement is explained as the amazing notion that one is not able to contradict or that contradiction does not exist. However, if this interpretation is right a problem arises, for it neglects the fact that Proclus said that according to Antisthenes it is ‘not necessary’ (μὴ δϵῖν) that one contradicts the other. The phrase ‘not necessary’ implies that there remain cases in which contradiction does actually exist. The number of cases, then, in which there is contradiction has only been reduced, but there positively remains the possibility that contradiction exists. Yet the current interpretation of the excluded contradiction according to Antisthenes has no provisos, an interpretation that could be supported if a slight change to the Greek is allowed and we read μηδ᾿ ϵἶναι instead of μὴ δϵῖν.