As Aristotle noted long ago, thought – or speech or reason – itself moves nothing, especially, one can add, thought merely laid down next to appetite. Thought, to be effective, must be inseparable from appetite.
The true source of action is not abstract thought, nor even thought applied to some separate motor or motive force, but rather a concretion, a grown-togetherness, of appetite and mind, so intertwined that one cannot say for sure whether the human principle of action is a species of desire become thoughtful, or an activity of intellection suffused with appetite. How mind and desire become grown together is, of course, a great question, but it is rarely accomplished by applying purely rational doctrines or rules in a passionless way to human agents. On the contrary, the true beginning is rather with the direct but unreflective education of our loves and hates, our pleasure and pains, gained only in practice, through habituation and by means of praise and blame, reward and punishment. Anyone concerned with influencing conduct must be concerned with these in-between powers of the soul, themselves irrational (in the sense of nonreasoning) but fully amenable to reason (in the sense of being formed, to begin with, in accordance with the reasons of one’s parents, teachers and laws, and being open to further refinement through the exercise of one’s own powers of deliberation and discernment).
Leon R. Kass – Life, Liberty, and the Defense of Dignity: The Challenge for Bioethics p.68