In an essay titled "How to Think about the Problem of Free Will", Peter van Inwagen writes:
‘free will’, ‘incompatibilist free will’, ‘compatibilist free will’, and ‘libertarian free will’ are four names for one and the same thing. If this thing is a property, they are four names for the property is on some occasions able to do otherwise. If this thing is a power or ability, they are four names for the power or ability to do otherwise than one in fact does. All the compatibilists I know of believe in free will. Many incompatibilists (just exactly the libertarians: that’s how ‘libertarian’ is defined) believe in free will. And it’s one and the same thing they believe in. Compatibilists say that the existence of this thing (whose conceptual identity is determined by the meaning of the English word ‘able’, or of some more or less equivalent word or phrase in some other language) is compatible with determinism; incompatibilists say that the existence of this thing is incompatible with determinism.
Reading this part surprised me at first. Is what Inwagen claiming here true and uncontroversial? Do 'compatibilist free will' and 'libertarian free will' by default mean one and the same thing? Don't incompatibilists routinely reproach compatibilists like Dennett for redefining 'free will' or for watering it down?
Also, Inwagen claims that 'free will' is a philosopher's term of art and is hardly used outside of a philosophical context. Is this how the majority of other philosophers see it? I'm not so sure myself. Dennett, for example, sees free will as a central folk concept belonging to our manifest image.