Peter van Inwagen: Libertarianism and incompatibilism

Peter Van Inwagen is a libertarian who believes that free will is incompatible with determinism. Many philosophers today accept that free will is compatible with causal determinism – the view, for very different reasons, of Hume and Kant. But, argues Inwagen, solving the problem of whether free will or determinism is true is really the problem of whether they are compatible. And in considering this question, w need carefully to define our terms. PB

Source    http://www.informationphilosopher.com/solutions/philosophers/vaninwagen/

Peter van Inwagen made a significant reputation for himself by bucking the trend among philosophers in most of the twentieth century to accept compatibilism, the idea that free will is compatible with a strict causal determinism.

Indeed, van Inwagen has been given credit for rehabilitating the idea of incompatibilism in the last few decades. He explains that the old problem of whether we have free will or whether determinism is true is no longer being debated. In the first chapter of his landmark 1983 book,An Essay on Free Will, van Inwagen says:

1.2 It is difficult to formulate "the problem of free will and determinism" in a way that will satisfy everyone. Once one might have said that the problem of free will and determinism — in those days one would have said 'liberty and necessity' — was the problem of discovering whether the human will is free or whether its productions are governed by strict causal necessity. But no one today would be allowed to formulate "the problem of free will and determinism" like that, for this formulation presupposes the truth of a certain thesis about the conceptual relation of free will to determinism that many, perhaps most, present-day philosophers would reject: that free will and determinism are incompatible. Indeed many philosophers hold not only that free will is compatible with determinism but that free will entails determinism. I think it would be fair to say that almost all the philosophical writing on the problem of free will and determinism since the time of Hobbes that is any good, that is of any enduring philosophical interest, has been about this presupposition of the earlier debates about liberty and necessity. It is for this reason that nowadays one must accept as a fait accompli that the problem of finding out whether free will and determinism are compatible is a large part, perhaps the major part, of "the problem of free will and determinism".
(Essay on Free Will, p.1)

Van Inwagen's Major Contribution – Incompatibilism

Just as Peter. F. Strawson in 1962 changed the subject from the existence of free will, from the question of whether determinism or indeterminism is true, and just as Harry Frankfurt changed the debate to the question of the existence of alternative possibilities, so Peter van Inwagen made a major change, at least in the terminology, to the question of whether free will and determinism are compatible, indeed whether free will entails determinism, as he says above.
Van Inwagen replaces the Traditional Problem of "liberty and necessity," finding out whether determinism is true or false, and thus whether or not we have free will, with a new problem that he calls the Compatibility Problem.

I shall attempt to formulate the problem in a way that takes account of this fait accompli by dividing the problem into two problems, which I will call the Compatibility Problem and the Traditional Problem. The Traditional Problem is, of course, the problem of finding out whether we have free will or whether determinism is true.

But the very existence of the Traditional Problem depends upon the correct solution to the Compatibility Problem

If free will and determinism are compatible, and, a fortiori, if free will entails determinism, then there is no Traditional Problem, any more than there is a problem about how my sentences can be composed of both English words and Roman letters. (Essay on Free Will, p.2)

Despite the obvious over-reaching claim that the Traditional Problem would disappear, which was nonsense, van Inwagen's new framing proved immensely popular over the next few decades. And the new framing introduced a new jargon term that is in major use today, the position of "Incompatibilism." Earlier writers, Carl Ginet and Wilfred Sellars, for example, had said that free will is "incompatible" with determinism. But that was simply the original position of all libertarians, in opposition to both the determinists and the compatibilists (William James' "soft' determinists), who were following what Sellars called the traditional Hume-Mill solution, which "reconciled" free will with determinism.