Dear Ray Harvey: Can you prove that humans possess the faculty of choice?
Dear Waffling: Yes, I can. And so can you. But first let me point something out: in the same way that you could not ever conceive dreaming if you’re never awake, so you can never conceive choice if you’re never actually able to choose. In other words, the fact that you’re even able to conceive of volition at all goes a very long way in proving it. Choice is an inherent — and definitional — part of the rational faculty, which humans alone possess.
While you’re at your computer right now, think of some small and inconsequential task you could perform — moving your mouse arrow to a certain quadrant of the screen, for instance, or tapping your spacebar once — but do not actually do it. Whatever the small task is that you conceive of, fix it in your mind for a moment. Observe yourself. Observe that in this moment you can choose to perform that small task, or you can choose not to perform it. You have an alternative, and your will alone is what will determine the outcome. Observe that what determines your choice is your decision to do it or not. That decision is your freedom of will. Quoting (again) the philosophical psychologist Rollo May:
When we analyze will with all the tools that modern psychology brings us, we shall find ourselves pushed back to the level of attention or inattention as the seat of will. The effort which goes into the exercise of will is really effort of attention; the strain in willing is the effort to keep the consciousness clear, i.e. the strain of keeping attention focused” (Rollo May, Love and Will, 1969).
Now, Waffling, decide, one way or the other, and then follow through with your decision.
That’s all the proof you need: direct observation. All knowledge starts and ends with observation.