Tooling around youtube I came along this video of an exercise Sam Harris offered as a practical refutation of free will.
The exercise Harris advocates is essentially this: He asks you to think of a city, any city, in the world, without any constraints. Once you have done so, Harris claims that this choice, if anything, would be an example of the exercise of free will. He then proceeds to debunk the choice as free by arguing that it wasn't really free. I won't rehearse all the reasons he provides (the video is only about 6 minutes), but his arguments all boil down to showing that the choice must have had a cause, even if we are unaware of the cause. For instance, you may have chosen Paris as your city because it happened to bubble up out of your subconscious, and that bubbling was a function of the fact that you once travelled to Paris and have fond memories. The point is that we mistakenly think the choice was "free" because we think we chose it arbitrarily, when in actuality the cause was driven by psychological factors of which we were simply unaware.
Harris's exercise involves a typical misunderstanding of what is meant by "free will", or rather, what the classical philosophers meant by calling man free. They did not mean that human will is an uncaused cause, which is what Harris seems to think it must mean. That would simply be to mistake man for God, Who is the only possible uncaused cause.
Man's will is classically understood to be free not because it is uncaused, but because it can have rational causes rather than irrational ones. Specifically, man can rationally judge means and the relationship of means to ends, and choose a course of action based on that judgement. (This is what Plato meant by saying "the truth shall make you free.") It is in the exercise of rationally considered action that man's freedom is manifest, not in the allegedly arbitrary choice of a meaningless selection as in Harris's exercise. A classical philosopher would not dispute that the choice made by a person in Harris's exercise is not free - in that sense, Harris is not showing anything new. But they would point out that they never thought such a choice was free in a significant sense in any case.
To flesh these points out, consider the difference between a beaver building a dam and a man building a dam. The beaver builds a dam by instinct. When it hears the sound of running water, it attempts to stop the sound by piling sticks and mud on it - even in cases where it makes no sense to do so. (For example, playing the sound of running water beneath a concrete floor will cause beavers to pile mud and sticks over the sound on the dry concrete). The beaver builds the dam the same way every time, by piling up sticks and mud, and will keep building them the same way.
The beaver is not free in its dam building. It's not free when it builds the dam (the end), because it simply starts building a dam at the sound of running water, nor is it free in how it builds (the means), for it does it the same way every time by piling up mud and sticks.
Now consider man building a dam, for example Hoover Dam. Man did not build this dam because he happened to hear the sound of running water once and automatically started piling sticks on it. The dam was built after a long, rational consideration of ends that might be achieved with the dam - hydroelectricity and the recreational possibilities of Lake Mead among others. Once the end was selected, the means were then considered. The dam could be build out of a variety of materials and in a variety of places. Concrete for the material was selected and a particular spot on the Colorado river was chosen - and not because an engineer picked the location "freely" by just letting a location pop into his head, but as the result of a detailed investigation of hydrology and the anticipated consequences of various locations.
Eventually the construction began and the Hoover Dam was built and it stands as a monument to the freedom of man, which means the freedom to know the truth and to act according to it. It doesn't mean to act in some purely arbitrary manner. That is the degenerate freedom that has unfortunately become the vision of freedom of that has captured the imagination of modern man.
Know the truth and it shall make you free.