Aristotle was of the opinion (Nicomachean Ethics, Book 6) that the aim or end of the process of willing is set only by our desires, and that reason is required to discover the means to achieve those ends. This was echoed by David Hume, who wrote, in Treatise on Human Nature, that "reason is and ought only to be the slave of the passions". Thus the ends at which we aim are determined by our innate instincts and preferences, leaving reason to assist only in finding the best ways to attain these ends.
This view has in the past been challenged in a variety of ways.
1. Sometimes the desire to act in a consistent manner and avoid contradiction - as it is sometimes called, to behave rationally - may override other desires. Thus a thief may feel a pang of pity for his victims, but he would very likely pull himself together by arguing that he should not allow his emotions to get in the way of pursuing his professional calling.
2. When there is a choice of desirable options to aim for, then reason will be called on to choose between them, so in that sense, reason could be said to be setting the aims in this situation.
3. A strong criticism of the theory is that it makes an artificial distinction between reason and desire which does not exist in practice. The mind exists and operates as a unity, with the "component" parts of it working together in a seamless manner.
4. Reason and reflection may suggest a course of action, and if this is later accompanied by a desire the action may be put into effect. Some might argue that desire is still the determining factor, but here, reasoning has also played a part.
5. Introspection (a reasoning process) may lead us to suspend our judgement, and leave the execution of a desirable course of action until a later time, after which it may happen that other considerations have arisen which will influence our desires. For example, if I write an angry letter to someone, it may happen that if I do not send it immediately, but perhaps wait until next morning, I may discover some rational considerations which make the sending of the letter seem less desirable.
These objections (and others) can lead us on to the possibility of our actions being determined, not so much by our desires and instincts, as by a "sense of duty" or conscience.
Socrates, who is often celebrated as the founder of Western philosophy, held that knowledge is virtue. In his view, a clear understanding of what is good would inevitably overcome all our other tendencies to action and thus would lead to right conduct.