One of these meanings is simply an expression of our own ignorance on the matter that happens to be before us. If I am asked what kind of weather we are likely to have a month hence, I should reply that it is equally possible the day may be dry or wet, bright or dull. I do not mean to imply that had I adequate knowledge it would not be as easy to predict the kind of weather on that date as it is to predict the position of Neptune. It is simply an expression of my own ignorance. But, as Spinoza pointed out, possibility narrows as knowledge grows. To complete ignorance anything is possible because the course of events is unknown. As a comprehension of natural causation develops, people speak less of what may possibly occur, and more of what will occur. Possibility here has no reference to the course of events, only to our knowledge, or want of knowledge, concerning their order. To say that it is possible for a man to do either this or that is, so far as a spectator is concerned, only to say that our knowledge concerning the man's whole nature is not extensive enough, or exact enough for us to predict what he will do. Nor is the case altered if instead of an outsider, it is the agent himself who is incapable of prediction. For all that amounts to is the assertion that the agent is ignorant of the relative strength of desires that may be aroused under a particular conjuncture of circumstances. The second sense of "possibility" depends upon our ability to imagine conditions not actually present at the moment of action. By a trick of imagination I can picture myself acting differently, or, on looking back, I can see that I might have acted differently. But in either case I have altered in thought the conditions that actually existed at the moment of action. Generally, all it means is that with a number of conflicting desires present, I am conscious that a very slight variation in the relative strength of these desires would result in a different course of conduct. And the conditions affecting conduct are so complex and so easily varied that it is small wonder there is lacking in this instance that sense of inevitability present when one is dealing with physical processes. But the essential question is not whether a slight change of conditions would produce a different result, but whether under identical conditions two opposite courses of action are equally possible? And this is not only untrue in fact, it is unthinkable, as a formal proposition. Even the old adage, "There, but for the grace of God, go I," while recognizing a different possibility, also recognized that a variation in the factors--the elimination of the grace of God--is essential if the possibility was to become an actuality. That the sense of possibility implies more than this may be safely denied, let who will make the opposite affirmation.