Freedom and Necessity, philosophy homework help

If I suffered from a compulsive neurosis, so that I got up and walked across the room, whether I wanted to or not, or if I did so because somebody else compelled me, then I should not be acting freely. But if I do it now, I shall be acting freely, just because these conditions do not obtain; and the fact that my action may nevertheless have a cause is, from this point of view, irrelevant. For it is not when my action has any cause at all, but only when it has a special sort of cause, that it is reckoned not to be free. A. J. Ayer, Freedom and NecessityWhat is the argument in the passage? And paraphrase the argument please.