Free will as a psychological errorNietzsche's critique of free will has essentially two aspects: one is philosophical (fatalistic), and the other is psychological.B. Leiter, Nietzsche's Theory of the Will, p. 1. Philosophers' Imprint v. 7, no. 7, September 2007. http://quod.lib.umich.edu/cgi/p/pod/dod-idx/nietzsche-s-theory-of-the-will.pdf?c=phimp;idno=3521354.0007.007 Online text here Fatalism lets Nietzsche theoretically prove the error of moral doctrines, which – most generally speaking – would require that a sinner changed his destiny (for instance by changing the laws of nature, influencing chances which lie completely beyond the extent of his influence), which is by definition impossible. But such theory would not be convincing enough if at the same time the impression of control was not removed, as well as the ever renewed attempts at associating it with the "freedom of will" and building a philosophy out of that. Thus a psychological critique is needed.
If one agrees that the "freedom of will" denotes the power of will which rules but is not itself ruled, then it would at bottom be enough to prove that it is not will what governs human behaviour in order to abolish the very term, to prove that "it is not there". And Nietzsche went on to this. For Nietzsche the term "will" is psychologically strictly connected with the term "aim" (he often combines the two), maybe even they are identical to him.Cf. The Will to Power, Book II ("Critique of highest values hitherto"), I. Critique of philosophy, 238: on "psychology which ... searched for will (i.e. aim) behind every act." Aim could then be interpreted, according to a common definition, as planning and intellectual foreseeing (of especially effects); according to Nietzsche first and foremost the anticipation of acts which in fact do not need to follow by its virtue from aiming (which is here foreseeing).
In Twilight of the Idols Nietzsche demonstrates the error of false causality just before the error of free will:
and then, in the section directly regarding free will, he observes:
Similarly in The Antichrist: "the will no longer «acts,» or «moves»...", "the term no longer denotes any power". This non-deriving of acts straight way out of aims, which are just foreseeing (the accompanying self-consciousness of that what is to come), but searching for their sources elsewhere (for example in reflexes, habits, urges) is to Nietzsche even one of major differences between medieval (Thomist) and modern psychology.
Nietzsche's words turned out to be prophetic, for modern neuroscience, especially the famous Libet's (or Kornhuber's) experiment and other of this type, has not once confirmed that the decision for an act is made beyond the (self)consciousness (in popular words, the will), which comes up to even half a second later.