In his “Nichomachean Ethics” Aristotle distinguishes between theoretical and practical knowledge. According to Aristotle, theoretical knowledge is knowledge is aimed at contemplation, it is the study of truth for it’s own value. It is knowledge of Practical knowledge, on the other hand, is knowledge about how to do things, how to live and act: “Since, then, the present inquiry does not aim at theoretical knowledge like the others (for we are inquiring not in order to know what virtue is, but in order to become good, since otherwise our inquiry would have been of no use), we must examine the nature of actions, namely how we ought to do them; for these determine also the nature of the states of character that are produced, as we have said” (Aristotle Book II, §2). While Aristotle favors theoretical knowledge and celebrates contemplative life of a philosopher as the greatest happiness achievable by men, he admits that it is practical knowledge, which supplies our daily needs and makes our life better, in this way making contemplative life possible.
It seems that Aristotle strictly separates theoretical knowledge from practical knowledge, but this distinction in real life is hardly sustainable. While theoretical knowledge is praised by him as “intellectual” activity, he implies that someone skilled in practical knowledge is not able to aspire for theoretical knowledge and vice versa. This belief is so deeply ingrained in present person’s consciousness that one can falsely assume that if he or she is skilled in some practical activity, he is not suited for theoretical activity, thus severely limiting his possibilities for self-fulfillment and self-development (Stanley).
The possible reason for people acting wrong or harming themselves and others even if they know what they do is harmful may lie in what Aristotle calls “passions”, which are related to kinds of knowledge and are the “roots” of all moral virtues. Aristotle points out that in order to be virtuous a person must abide to average, normal amount of these passions (fear, confidence, anger etc.). Any excess and defect in those passions depends on person’s choice, lying in a mean (Aristotle Ch22, §6). Thus, through choice a person can act wrongly or harmfully to himself or others even if his knowledge forbids that course of action.
Aristotle. Life of Excellence: Living and Doing Well. Web. 14 July 2013. <http://philosophy.lander.edu/intro/articles/aristotle-a.pdf>
Aristotle. Nichomahean Ethics. Web. 14 July 2013. <http://people.bu.edu/wwildman/WeirdWildWeb/courses/wphil/readings/wphil_rdg09_nichomacheanethics_entire.htm>
Stanley, Jason. The Practical and the Theoretical. May 6 2012. Web. 14 July 2013. <http://opinionator.blogs.nytimes.com/2012/05/06/the-practical-and-the-theoretical/>