Normative theories of argumentation tend to assume that logical and dialectical rules suffice to ensure the rationality of argumentative discourse. Yet in everyday debates people use arguments that seem valid in light of such rules but turn out to be biased and tendentious nonetheless. I review some of the empirical evidence indicating that people’s inferential reasoning is systematically affected by a variety of cognitive and motivational biases. I argue that there are privileged links between specific types of biases and specific types of fallacies. Insofar as such cognitive illusions are typically unintentional, it appears that arguers may be biased despite their well-intended efforts to follow the rules of critical argumentation. That being said, I claim that arguers remain partly responsible for the rationality of their arguments, inasmuch as there are different strategies of “argumentative self-control” that they can adopt if they wish to counteract their irrational attitudes in debate.