An argument can be taken as an operation of justification or as the product of this operation. But what about a counter-argument? This article is based on the hypothesis that there exists an operation of argumentative negation, which is both the argumentative and the negative equivalent of the operation of justification. Justification and argumentative negation necessarily act on assertions, for they are active at the level of the epistemic modalities of statements. As an operation, a counter-argument can thus be described, (...) as the application of an argumentative negation; as a product, it can be described as an argument the conclusion of which shows traces of negative modality. Two uses of argumentative negation are distinguished here: counter-argumentation and calling into question. The former can lead only to assertive conclusive statements, but the latter can also lead to directives or commissives. This leads the authors to introduce the notion of pseudo-argument, besides those of argument and counter-argument. It is shown in particular that when a pseudo-argument is rejected, argumentative negation has the effect of making evident an underlying argument. With respect to the latterit functions as a counter-argumentation, whereas with respect to the illocutionary act accomplished by the conclusive statement, it functions as a calling into question of a condition of satisfaction for this act. This article also defines certain characteristics of argument, proposes criteria for identifying argumentative negation in polemical conversations, and distinguishes four modes of counter-argumentation. (shrink)