 The most radical a priori argument is that free will is not merely contingently absent but is impossible. Nietzsche 1886 [1966] argues to this effect, and more recently it has been argued by Galen Strawson (1986, ch. 2; 1994, 2002). Strawson associates free will with being ‘ultimately morally responsible’ for one’s actions. He argues that, because how one acts is a result of, or explained by, “how one is, mentally speaking” (\(M\)), for one to be responsible for that choice one must be responsible for \(M\). To be responsible for \(M\), one must have chosen to be \(M\) itself—and that not blindly, but deliberately, in accordance with some reasons \(r_1\). But for that choice to be a responsible one, one must have chosen to be such as to be moved by \(r_1\), requiring some further reasons \(r_2\) for such a choice. And so on, ad infinitum. Free choice requires an impossible infinite regress of choices to be the way one is in making choices.