In metaethics there is major disagreement between the nature of moral facts and duties motivating an agent to conform to them. Beliefs should always motivate an agent to action. For example: if Billy understands one ought not to steal, then Billy is motivated via reasoning not to steal says the internalist. However, Billy can understand the moral obligation without consenting to its demand upon him says the externalist. But Kant retorts, if Billy really understands the nature of stealing, he would not be neutral on the matter but would instead be motivated by reason to stand against it.
The best option would be to affirm beliefs can motivate an agent to act but the agent can override them by other beliefs that motivate him/her. So it turns out both internalism and externalism capture one aspect of of how an agent's beliefs can motivate actions.