We are rational creatures, in that we are beings on whom demands of rationality are appropriate. But by our rationality it doesn't follow that we always live up to those demands. In those cases, we fail to be rational (and it is appropriate to use the term ‘irrational’), but it is in a way that is different from how rocks, tadpoles, and gum fail to be rational. For them, we use the term ‘arational.’ They don't have the demands, but we do. The demands of rationality bear on us because we have minds that can move us to act, inspire us to create, and bring us to believe in ways that are responsible and directed. My interests here are the demands rationality places on our beliefs. Beliefs aim at the truth, and so one of the demands of being a rational creature with beliefs is that we manage them in a way that is pursuant of the truth. Reasons and reasoning play the primary role in that management – we ought to believe on the basis of good reasons. That is, if you believe something, you think that you're right about the world in some way or another. You believe because you think that something (call it ‘p’) is true. Now, p's truth is different from all ways it could be false, and your being right about p isn't just some arbitrary commitment, one that could just as well have been its negation. This non-arbitrary specificity of beliefs is constituted by the fact that they are held on the basis of reasons. Arguments are our model for how these reasons go – we offer some premises and show how they support a conclusion. Of course, arbitrary premises won't do, so you've got to have some reason for holding them as opposed to some others. Every premise, then, is a conclusion in need of an argument, and for arguments to be acceptable, we've got to do due diligence on the premises. This, however, leads to a disturbing pattern – for every premise we turn into a conclusion, we've got at least one other premise in need of another argument. Pretty soon, even the simplest arguments are going to get very, very complicated.