Akrasia refers to the phenomenon of acting against one's better judgment—the state in which one intentionally performs an action while simultaneously believing that a different course of action would be better. Sometimes translated as "weakness of will" or "incontinence," akrasia describes the paradoxical human experience of knowingly choosing what one judges to be the inferior option.

In Plato's Protagoras dialogue, Socrates asks precisely how it is possible that, if one judges action A to be the best course of action, why one would do anything other than A.

In Plato's Protagoras, Socrates presents a radical thesis that fundamentally denies the existence of akrasia. His famous declaration, "No one goes willingly toward the bad" (οὐδεὶς ἑκὼν κακός), encapsulates a view known as Socratic intellectualism.

According to Socrates, genuine akrasia is impossible because human action necessarily follows knowledge. His argument proceeds through several interconnected premises:

Given the above premises, Socrates concludes that it is psychologically impossible for someone who truly knows what is best to act otherwise. The person who possesses genuine knowledge of the good will inevitably pursue it, as this pursuit aligns with both human nature and rational necessity.

Therefore, in the Socratic framework, what appears to be akrasia—acting against one's better judgment—is actually a form of ignorance. Actions that seem to contradict what is objectively best must result from incomplete knowledge of the facts, inadequate understanding of what constitutes the genuine good, or failure to properly calculate the consequences of one's actions.

Aristotle recognizes that the possibility of acting contrary to one's best judgment is a staple of commonsense and a common human experience. Aristotle dedicates Book VII of the Nicomachean Ethics to an examination of akrasia, adopting a distinctly empirical approach that contrasts sharply with Socratic intellectualism. He distanced himself from the Socratic position by distinguishing different mental faculties and their roles in action. He argues that akrasia results from the one's opinion (δόξα, doxa), not one's desire (epithumia) per se. The crucial difference here is that while desire is a natural condition of the body incapable of truth or falsity, opinion is a belief that may or may not be true, a cognitive state. Therefore, akratic failures can be explained by the incorrectness of one's best judgment rather than a failure to attempt to act according to one's best judgment. When an agent's best judgment is a false belief, it does not have the power to compel one that Socrates attributed to knowledge of what is genuinely best.

For Aristotle, the opposite of akrasia is enkrateia, a state where an agent has power over their desires. Aristotle considered one could be in a state of akrasia with respect to money or temper or glory, but that its core relation was to bodily enjoyment. Its causes could be weakness of will, or an impetuous refusal to think. At the same time he did not consider it a vice because it is not so much a product of moral choice as a failure to act on one's better knowledge.