If an agent judges that she morally ought to Φ in certain circumstances C then, according to internalists, absent practical irrationality, she must be motivated, to some extent, to Φ in C. Internalists thus accept what I have elsewhere called the “practicality requirement on moral judgement.” Externalists deny this. They hold that agents may not be motivated to any extent to act in accordance with their moral judgements, and this without any irrationality on their behalf.

Internalism has traditionally been thought to function as a high-level conceptual constraint on moral judgement, accounts of which are supposed to be assessed, inter alia, by the extent to which they can explain and capture its truth. Unfortunately, however, on closer inspection this doesn't amount to much in the way of a constraint. There are many different theories about the nature and content of moral judgement that aspire to explain and capture the truth embodied in internalism, and these theories share little in common beyond that aspiration.

Worse still, as I will argue in what follows, these theories are perhaps best thought of as lying around the perimeter of a wheel, much like Fortune's Wheel, with each theory that lies further on along the perimeter representing itself as motivated by difficulties that beset the theory that precedes it. The mere existence of Internalism's Wheel need not pose a problem for internalists, of course. They may believe that the truth about ethics lies wherever Internalism's Wheel stops spinning.