I lift my arm and let it fall. My action seems to me free; but asking myself whether I could raise my arm in every direction, I see that I raised it in the direction in which there was least obstruction to that action either from things around me or from the construction of my own body. I chose one out of all the possible directions because in it there were fewest obstacles. For my action to be free it was necessary that it should encounter no obstacles. To conceive of a man being free we must imagine him outside space, which is evidently impossible.
