New data could conceivably disprove Libet’s results, but the correction would mean nothing metaphysically because at the end of the day, Libet’s contribution was conceptual. Libet solved the mind-body problem en passant; his data forced him to grasp the distinction between the deciding experience and deciding itself, but the data themselves are metaphysically otiose. For metaphysics, Libet’s experimental results serve only as scaffolding for distinguishing deciding from decision and showing that temporal associations in the experience of deciding explain why we feel we exercise mentalistic control. The perception of deciding to act, distinct from the fact of acting, both explains the impression that we have free will and demonstrates free will’s untenability. The objective temporal ordering doesn’t bear on these distinctions and explanations—as long as the experience is that the act of will preceded or coincided with the act of deciding.
Libet (somewhat unknowingly) showed how human experience creates a predilection for a misplaced, impossible, perceived causal relation, and connections experienced create the causal illusion; real temporal relations are irrelevant. Simplicity recommends this explanation of phenomenal free will, and the explanation displays exactly why free will is illusion: sensations don’t cause physical events. Holding that experience interacts with the physical world, Descartes was the only important metaphysician to disagree, and every metaphysician today holds that two substances essentially different can’t interact. Physical laws govern physical events and leave no room for entry of purely mental causes.
A possible source of confusion about these arguments is metaphysicians’ acceptance of one class of mental causes, beliefs and desires. In response—perceiving willful efficacy differs from attributing beliefs and desires, in that nothing in the concept of “belief” and “desire” identify them as phenomenal experience. While belief and desire aren't experiences—available for association with other experiences—the error of considering beliefs experiential, held even by metaphysicians until the 20th century, may have generalized from free will to nonexperiental mental entities like belief and desire, causing the naive error that beliefs and desires are experiential.
Finally, since (if) sensations are brain events, one might contend that associating experienced decisions with actual action results in no anomalous causation. First, nothing in the experience of deciding points to the under-strata, and conditioning usually can target only phenomena. Second, if the objection holds, it’s at the expense of the mind-brain-identity theory’s credibility, in its insistence on a direct relationship between phenomenology and physics.
Next essay: Why free will?