Hume’s effort to draw a distinction between free and unfree (i.e., compelled) action itself rests on a distinction between internal and external causes. Critics of compatibilism argue that this – attractively simple – distinction is impossible to maintain. It seems obvious, for example, that there are cases in which an agent acts according to the determinations of his own will but is nevertheless clearly unfree. There are, in particular, circumstances in which an agent may be subject to, and act on, desires and wants that are themselves compulsive in nature (e.g., as with a drug addict or kleptomaniac). Desires and wants of this kind, it is claimed, limit and undermine an agent’s freedom no less than external force and violence. Although it may be true that in these circumstances the agent is acting according to his own desires or willings, it is equally clear that such an agent is neither free nor responsible for his behavior. It would appear, therefore, that we are required to acknowledge that some causes “internal” to the agent may also be regarded as compelling or constraining. This concession, however, generates serious difficulties for the classical compatibilist strategy. It is no longer evident, given this concession, which “internal” causes should be regarded as “constraining” or “compelling” and which should not. Lying behind this objection is the more fundamental concern that the spontaneity argument presupposes a wholly inadequate understanding of the nature of excusing and mitigating considerations.