According to one of the most influential and popular theories in the
contemporary theory of action, an agent S is motivated to perform a certain
act A if and only if she endorses some set of reasons R on the basis of which
it follows that she should perform A, and given that she does not suffer from
some sort of practical irrationality (e.g. depression, weakness of will,
psychopathy, mental or physical exhaustion etc.). At least at first glance,
this theory - which is known as the rationalist motivational internalism -
appears to be uncontroversial and unproblematic. Yet, over the past ten
years, this popular position has faced numerous very serious objections. In
the course of this work, I intend to present some of these objections, in
order to justify the claim that the concept of practical irrationality - i.e.
the concept that plays the central role in this particular version of
internalism - should be left out from the philosophical explanation of
motivation. I will then attempt to defend the conclusion that the rationalist
motivational internalism represents a completely inadequate theory of
motivation.