 Clarke attached great importance to the issue of free will, and he may have introduced the modern philosophical meaning of the term “agency” (Schneewind 1997, 313). In his philosophical writings, he argues that freedom of the will involves a libertarian power of self-determination. However, in the sermon “Of the Liberty of Moral Agents,” he claims that the “True liberty of a Rational and Moral Agent” is “being able to follow right Reason only, without Hindrance or Restraint” (W 1.219). Similarly, in that sermon Clarke calls acting as one pleases “mere physical or natural liberty” (which humans and non-human animals have), so he seems to accept a definition of liberty that is compatibilist (W 1.218). Elsewhere he argues that human freedom requires a self-determining will that could freely assent or refrain from assenting to the mind’s judgments; this is a freedom of choosing and not a freedom of acting, such that a prisoner in chains “who chooses or endeavors to move out of his place is therein as much a free agent as he that actually moves out of his place” (D 75, W 2.566). Clarke does not explicitly reconcile these incompatibilist and compatibilist approaches. One way to do so is to make the libertarian power of self-determination a necessary condition for the compatibilist understanding of freedom as following reason without restraint. Clarke also entertains a third notion of freedom: freedom is “a principle of acting, or power of beginning motion, which is the idea of liberty” (D 54, W 2.553). The ability to begin motion marks freedom as a power only held by non-material agents, because matter has no power of self-motion. This third definition is libertarian and is probably the most important of the three to Clarke’s project (Harris 2005, 46–61; Greenberg 2013, 249–251).