With the advent of psychology and later neuroscience, many theories of action are now subject to empirical testing.
In the simple theory (see Donald Davidson), the desire and belief jointly cause the action.
Michael Bratman has raised problems for such a view and argued that we should take the concept of intention as basic and not analyzable into beliefs and desires.
However, many theories of action argue that rationality extends far beyond calculating the best means to achieve one's ends.
Rationality, in such theories, also involves responding correctly to the reasons an agent perceives, not just acting on wants.