Stace is a ‘compatibilist’, meaning that he believes freedom to be compatible with causal determinism. His position is that for a behavior to be free is not for it to be uncaused but is rather for it to be caused in a certain way by one’s mental condition. If I black out and, while falling, hit my head on the light switch, thereby causing the lights to turn off, I did not freely turn off the light, for the reason that, even though I did turn off the light, my doing so did not appropriately result from my psychological condition. (It may well be that it did result in some way or other from my psychological condition; it may be that my blacking out, and therefore my accidentally turning off the light, was a consequence of my choosing to drink alcohol. But it did not appropriately result from my psychological condition, being more in the nature of an accidental by-product of it.) By contrast, if, while in full possession of my faculties, I coolly and deliberately flip the switch, knowing that doing so will cause the lights to off, then I have freely turned off the light, since in this case the operative behavior did appropriately result from my psychological condition.
The standard objection to this position is as follows. If the world is deterministic, then our actions are the inevitable result of forces that lie outside our control and we are therefore not responsible for them. But there is a flaw in this reasoning. To be sure, if the world is deterministic, then our actions result from forces outside of our control. But sometimes those forces operate via our agency, this being our ability to decide how to act, and when this happens, the resulting actions are free.