Aristotle, Nicomachean Ethics
H. Rackham, Ed.

[2] Now the activities of the intellect differ from those of the senses, and from¹ one another, in kind: so also therefore do the pleasures that perfect them.

This may also be seen from the affinity which exists between the various pleasures and the activities which they perfect. For an activity is augmented by the pleasure that belongs to it; since those who work with pleasure always work with more discernment and with greater accuracy—for instance, students who are fond of geometry become proficient in it, and grasp its various problems better, and similarly lovers of music, architecture or the other arts make progress in their favorite pursuit because they enjoy it. An activity then is augmented by its pleasure; and that which augments a thing must be akin to it. But things that are akin to things of different kinds must themselves differ in kind.