What is the relationship between appetite and inclination? How does the distinctively rational character of the will correspond to its function within the operations that sustain human life? Finally, how are our actions determined by this rational will?

The will is the capacity to desire and pursue one’s own overall existence and full development in accordance with some reasoned conception of what it means to live an appropriate, or desirable, or ideal human life. Other kinds of animals neither have nor need this kind of capacity, because their passions naturally operate in such a way as to generate appropriate, beneficial behavior. Our passions cannot play a similar part in our own lives, even after they are informed by habits, because they are not sufficiently integrated to work together in a coordinated way to promote our overall good. Over and above the specific desires generated by the passions, the human person needs an overarching desire to exist, and to live and flourish in an appropriate way – which is to say, she stands in need of the appetite of the will, which provides the impetus for action throughout her life.

We can now begin to see how Aquinas situates the will within the context of his overall metaphysical account of existence, operation, and perfection. The inclinations of the will are naturally oriented towards goods that are in some way an expression and extension of the creature’s full actuality, or in other words, its perfection. Understood in these terms, the will is essentially similar to any other appetite, including the appetites of non-living creatures. More specifically, the will is an appetite of a living, sentient creature, that is to say, an animal. As such, its operations depend on some kind of conscious awareness of a desirable object, which calls forth an inclination of desire, thus moving the creature to action. A distinctive kind of rational appetite that characterizes human existence, the will depends for its operations on a reasoned, abstract conception of one’s good, eliciting inclinations towards those objects which the agent judges to be necessary to, or appropriately suited to, the attainment and enjoyment of that good. Aquinas holds that every rational agent necessarily desires its perfection and directs all his or her activities towards the attainment or enjoyment of that end. And since–as he also believes–the perfection of a rational creature is equivalent to its happiness, this is equivalent to saying that everyone necessarily desires happiness and directs all actions, in some way or other, towards that end.

When we move from the operations of natural appetite to the inclinations and operations of the higher animals, we encounter a distinctively new kind of activity, corresponding to a new level of normativity. Similarly, the operations of rational creatures introduce a new level of activity, and correspondingly, a new level of normative considerations. The other higher animals can be said to move themselves to act, insofar as they act out of inclinations elicited by objects held within their own consciousness. The rational creature, in contrast, acts out of a reasoned, self-reflective conception of his overall good, comprehensively considered. Aquinas brings this point out in the context of comparing the diverse ways in which different kinds of creatures are subject to divine providence.

As he explains, all creatures are subject to God’s providence, which unfolds through the dynamic operations of the specific forms of existence in which each is created – thus, creatures can be said to desire and seek God, simply because of their natural or sensual appetites for their own perfection. The same may be said of the rational creature, but Aquinas adds an important qualification: “Among the rest, however the rational creature is subject to divine providence in a more excellent way, insofar as he becomes a participant in providence, being provident for himself and others.” In contrast to other kinds of animals, then, the human person is capable of thinking about herself as the subject of a kind of life, reflecting on what it would mean to live well, and reflectively desiring and choosing activities in accordance with her overall aims. Indeed, without some degree of reflection on her aims and activities, the human person cannot live an independent, properly human life at all.

The distinctively human capacity for self-reflective activity opens up possibilities for self-evaluation and appraisals of others’ conduct, in accordance with objective, mutually acknowledged standards. As we noted above, non-human animals act in accordance with normative standards of the pleasant and the unpleasant, and the criteria for their overall success are determined by natural tendencies to live and reproduce. Rational agents, on the other hand, act in accordance with normative standards of the reasonable and the unreasonable, or what is contrary to reason. These standards open up new kinds of normative practices, grounded in giving reasons for one’s actions, offering rational objections to the actions of another, demanding something on the basis of a reasonable claim, and the like. These practices, in turn, go along with fundamental moral concepts such as responsibility, accountability, and authority, each of which implies some kind of demand or justification for conduct framed in terms of one’s reasons for acting. In other words, the distinctively human capacity for self-reflective activity allows us to think and act with an eye to something we understand, along with others, as “right” or “wrong.”