Argumentation is considered here as discourse that involves arguments, defined as reason(s) - conclusion pairs. In an argument, reasons are oriented in favor of the conclusion. It can happen that an argument is used to argue against the conclusion of another argument. This article is devoted to this negative aspect of argumentation, which has seldom been studied elsewhere. After insisting on the dialogical dimension of every argumentation, the hypothesis is developed that an argument is accepted only if the reasons it provides seem plausible, relevant, oriented in favor of the conclusion, and sufficient to support it. An attempt is then made to show how an argument can be refuted by objections to any one of these parameters. In particular, these modes of counter-argumentation are studied from the point of view of their effects on the conclusion. Finally, other procedures of negative argumentation are presented that are not, strictly speaking, counter-argumentations, for they do not directly concern the reasons of the disputed argument. This is the case of discrediting an opponent or making a claim of misunderstanding.