Good reasoning is often reduced to deductive validity. This is a mistake. If we pay a peculiar attention to how human beings actually draw conclusions, we must recognize that correct arguments are not always deductively valid, and even that deductively valid arguments are not always correct. Whether it be concerned with e.g. generic reasoning, abduction, or even how to handle inconsistencies, defeasible reasoning explains how non-deductively valid arguments can have a cognitive virtue.