Various philosophers have offered just such an account of freedom. Thomas Hobbes suggested that freedom consists in there being no external impediments to an agent doing what he wants to do: “A free agent is he that can do as he will, and forbear as he will, and that liberty is the absence of external impediments.” In An Enquiry Concerning Human Understanding, David Hume thought that free will (or "liberty," to use his term) is simply the “power of acting or of not acting, according to the determination of the will: that is, if we choose to remain at rest, we may; if we choose to move, we also may.… This hypothetical liberty is universally allowed to belong to everyone who is not a prisoner and in chains.” This suggests that freedom is simply the ability to select a course of action, and an agent is free if he is not being prevented by some external obstacle from completing that course of action. Thus, Hobbes and Hume would hold that Allison is free to walk her dog so long as nothing prevents her from carrying out her decision to walk her dog, and she is free not to walk her dog so long as nothing would compel her to walk her dog if she would decide not to.