We need to consider the relation, within the mind, between desires and thought. That relation should be the same as that between willing and understanding, since we generally think that willing is in accordance with our desires and with our loves and motivations: we will by means of desires. We also generally think that our understanding is in accordance with our thought: we understand by means of our thoughts and ideas.
But does desire generate thought, or thought generate desire, or neither? There is room for debate on this, but there are psychological, philosophical and theological arguments to lead to the conclusion that it is desire which generates thought, rather than the opposite.
The psychological evidence stems from the fact that persons tend to think about what they want: their desires lead their dreaming, thinking, planning and eventually acting to get what they want. This suggests that desires generate the streams of thought that occur in the understanding, rather than that our thinking dictates what we want, love, or desire. Thought may influence what we desire but only by selection. Our thoughts select which desires can be feasibly brought nearer satisfaction.
Some will disagree, saying that it is primarily thought that makes our desire, and that we tend to desire things that we have thought up. This is true, but what is the causal determiner of what we think up? Thoughts seem to pop into our heads, and thoughts about what we desire are much more likely to do so! We interfere at this point sometimes and reject thoughts as unsuitable, but that rejection itself also requires motivation or desire. We do not clearly see our desires in our consciousness, but only our thoughts and actions, so we tend to forget about the essential role of dispositions and desires.
How many times have we seen people, seeming to themselves to be rational, being driven by desires which they hardly acknowledge existing?
Philosophically, we could argue from the Aristotelian view that thought is the entertaining of the forms of things. Then, since forms themselves have no causal power, we could say that all the power must belong to whatever is doing the thinking and not to the thoughts themselves. This implies that thoughts themselves are not dispositions. The honor of being dispositions belongs to desires or loves. Desires are more similar to dispositions than are thoughts. It is dispositions (rather than forms) which are causally efficacious.
This agrees in general with the analysis of Gilbert Ryle's 1949 book "The Concept of Mind". He argues that minds as a whole are akin to dispositions, and hence the actions of a person are the effects of those dispositions. He took this to imply materialism, but we will see later that other conclusions are possible, even preferable.