Aristotle, and W. Rhys Roberts. Rhetoric. Mineola, NY: Dover, 2004. Kindle Electronic Edition.
Book II, chapter 19.
Aristotle writes about the relation of that which is possible and that which is impossible. He first reminds the reader “that if it is possible for one of a pair of contraries to be or happen, then it is possible for the other (Aristotle II.19, B 1392a). For example, if someone can be cured he can become il. If a harder thing is possible, so is the easier. If a beautiful house can be built, a house in general can be built. If an outcome is possible, so is its cause. Aristotle also looks at matters of “past fact” (Aristotle II.19, B 1392b). Again considering two related events, if the less likely has occurred, it is likely that the more likely has also. If an outcome usually happens, it is likely to have happened in the past. To determine future fact we use the same process (Aristotle II.19, B 1393a). If there is both desire and ability to do something it will be done. If it is normal for something to happen now and in the past, it is likely in the future.