This article is a critique of Aristotle's refutation of the opponents to the Principle of Non-Contradiction (PNC). I try to shed light upon five errors in his demonstration. Firstly, it is not necessary to give up demanding that the opponent utter a complete sentence (and not a mere word) at the beginning of the demonstration. Secondly, Aristotle silently passes from «meaning» to «meaning something well-defined» in his demonstration. Thirdly, the demonstration being inductive, it cannot claim to be universal. Fourthly, Aristotle is not faithful to his own definition of «meaning». Fifthly, Aristotle's refutation does not take into account the specificity of the opponents to the PNC. Finally, I draw attention to the fact that Aristotle argues without postulating reciprocity between himself and his interlocutor. This invalidates a part of his argumentation, that part precisely in which he assumes that when the petitio principii is commited by the adversary, it constitutes more than a petitio prin- cipii.