In this essay, I first discuss the conditions set by theorists of democratic deliberation on proper deliberation. These conditions call for reasoned decisions from mutually acceptable premises. Next, I present the ideal of critical thinking that should guide the citizen in this deliberation. I then examine the empirical literature on human reasoning. Some research results in the empirical literature paint a bleak picture of human rationality: we fall victim to heuristics and biases, persevere in our beliefs in the face of (...) contrary evidence, and justify our moral judgments by post hoc-reasoning. In addition, the deliberating groups have problems of their own. The groups may, for example, amplify errors or fall victim to information cascades. Though these epistemically detrimental processes can be overcome, they do present a challenge to our rationality. The essay concludes by arguing that the empirical evidence in fact supports an internalistic approach to group deliberation, a claim challenged by Solomon. (shrink)