To these two modes of occupation, with their distinction of servile and free activities (or "arts") correspond two types of education: the base or mechanical and the liberal or intellectual. Some persons are trained by suitable practical exercises for capacity in doing things, for ability to use the mechanical tools involved in turning out physical commodities and rendering personal service. This training is a mere matter of habituation and technical skill; it operates through repetition and assiduity in application, not through awakening and nurturing thought. Liberal education aims to train intelligence for its proper office: to know. The less this knowledge has to do with practical affairs, with making or producing, the more adequately it engages intelligence. So consistently does Aristotle draw the line between menial and liberal education that he puts what are now called the "fine" arts, music, painting, sculpture, in the same class with menial arts so far as their practice is concerned. They involve physical agencies, assiduity of practice, and external results. In discussing, for example, education in music he raises the question how far the young should be practiced in the playing of instruments. His answer is that such practice and proficiency may be tolerated as conduce to appreciation; that is, to understanding and enjoyment of music when played by slaves or professionals. When professional power is aimed at, music sinks from the liberal to the professional level. One might then as well teach cooking, says Aristotle. Even a liberal concern with the works of fine art depends upon the existence of a hireling class of practitioners who have subordinated the development of their own personality to attaining skill in mechanical execution. The higher the activity the more purely mental is it; the less does it have to do with physical things or with the body. The more purely mental it is, the more independent or self-sufficing is it.