Abstract
Aristotle gives an account of pleasure in two different treatises of the Nicomachean Ethics. In book VII he identifies pleasure with the pleasurable activity, while in book X he treats pleasure as something different from the pleasurable activity. These two treatises give two ways to study pleasure from a philosophical point of view. We can ask for the conditions that an activity must fulfil to be pleasurable or we can ask for the metaphysical category of pleasure. In this paper I try to answer to these questions and to approach to Aristotle's concept of pleasure, relating the concept of >ἐνέργεια’< that Aristotle uses in book X with the self-perception and the perfection of the vital activities.