205. Nevertheless my explanations appear to be at least morally certain. . .
Something can be morally certain, i.e. sure enough for everyday practical purposes, while still being uncertain in relation to the absolute power of God. Without having been to Rome (let’s suppose), you are sure that it is a town in Italy, but it could be the case that everyone who has told you this has been lying. ·And here’s another example·. You are trying to read a document written in Latin but encoded; you guess that every ‘a’ should be a ‘b’, every ‘b’ a ‘c’, and so on through the alphabet, and when you decode the document on that basis it makes good sense. You won’t doubt that you have detected the code and understood the letter—·you’ll be morally certain of that·. But it is possible that you are wrong, and that the document involves some other code and means something different from what your decoding made it mean. •Possible, but hardly •credible—especially if the document is long. Well, now, look at all the many properties relating to magnetism, fire and the fabric of the entire world that I have derived in this book from just a few principles: you may think that my assumption of these principles was arbitrary and groundless, but perhaps you’ll admit that if my ‘principles’ were false it would hardly have been possible for them to fit so many items into a coherent pattern.
206. . . . and indeed more than morally certain.
Besides, even in relation to nature there are some things that we regard as not merely •morally but •absolutely certain. (Being absolutely certain that P involves thinking that it’s wholly impossible that P should be false.) This certainty has a metaphysical basis in the proposition that God is supremely good and in no way a deceiver, and hence that the faculty he gave us for distinguishing truth from falsehood can’t lead us into error while we are using it properly and are thereby perceiving something clearly. Mathematical demonstrations have this kind of certainty, and so does the knowledge that material things exist, as does all evident reasoning about material things. If you think about how I have reached •my results, deriving them in an unbroken chain from the first and simplest principles of human knowledge, you may be willing to count •them among the absolute certainties. You are especially likely to do so if you have a proper grasp of two facts: (1) We can have no sensory awareness of •external objects unless •they make something move in our nerves; and (2) the fixed stars, owing to their enormous distance from us, can’t produce such motion ·in our nerves· unless some motion is also occurring both in them and also throughout the entire intervening part of the heavens. [Strictly, the ‘enormous distance’ clause shouldn’t occur in that sentence; Descartes’s considered view is that something six inches from us can’t stimulate our nerves unless there is motion in it and through the intervening space.] Once this is accepted, it seems that all the other phenomena, or at least the general features of the universe and the earth that I have described
In my opinion absolute certainty is not possible. Moral certainty is the best we can do. Moral certainty is open to critique and analysis. Decisions and actions are necessary. Judgement is needed to analyze the aspects of certainty pertinent to a given decision. Good judgement is the ability to make decisions acceptable to God.