Many philosophers think that whenever we are motivated to act, our motivation always involves a belief. E.g. according to the version of the Humean Theory of Motivation that is defended by Michael Smith, your motivation for action always consists of a desire and a "means-end belief" (see The Moral Problem, p. 92).
I think this is false. There are cases in which for no further reason, you simply form an intention to perform a certain basic action right now. Then I think that this intention can motivate you to act, without the need for any "means-end belief" at all.
E.g. suppose that I am walking along by myself, and for no particular reason, I just form the intention to raise my arm right now.
Now, raising my arm right now is a basic action for me (to use Arthur Danto’s famous term). It is something that I can just do. I can simply raise my arm without doing anything else (or at least without intentionally doing anything else) as a means to raising my arm. So surely no "means-end" belief is involved in the process that leads from my intention to raise my arm right now to my raising my arm now.
It would be wrong to say, it seems to me, that I must have the belief ‘This is a way for me to raise my arm’ (where ‘this’ corresponds to one of the special "practical modes of presentation" that are discussed by Jason Stanley and Timothy Williamson in their 2001 JPhil paper "Knowing How"). After all, what difference would it make for me to have this belief, until this belief helped to motivate me to form a further intention — viz. the intention to do this? But then if it was necessary for me to have the means-end belief ‘This is a way for me to raise my arm’ in order to carry out the intention to raise my arm, why isn’t it necessary for me to have a further means-end belief, of the form ‘This1 is a way for me to do this2‘, in order to carry out the intention to do this2? But now we seem to be launched on an infinite regress…
So I think that we must recognize that an intention to do a basic action right now can lead directly to action, without needing the cooperation of any "means-end" belief, or indeed any other belief at all.
Moreover, I also don’t see why my original adoption of this intention need have been motivated by any antecedent belief either. I just decide to raise my arm because I feel like it. Perhaps it is true that as a (more or less) rational agent, I wouldn’t have adopted this intention if I had held any beliefs that would have made it rational for me to believe that there was a good reason for me not to raise my arm. That is to say, the way in which I form this intention is sensitive to the absence of beliefs that should have motivated me to do otherwise. But this is not the same as my being motivated by the presence of any beliefs that I actually hold.
So I conclude that beliefs are just not necessary for motivation at all. Intentions can suffice for motivation all by themselves.