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The main issue of this chapter is then, what are proper stopping-points for explanation, when do we have grounds for supposing that certain phenomena constitute such stopping-points and when do we have grounds for supposing that they themselves have an explanation. Having established general principles, we can then ask whether it is right to suppose that the physical universe, or the regular operation of scientific laws, or such particular events as (assuming that it happened) the resurrection of Christ from the dead, are just brute facts, or whether they are phenomena which it is reasonable to suppose to have a further explanation. Before I come to deal properly with the central issue, I need first to make certain distinctions. The question of what is a 'terminus' of explanation needs a more technical explication. And partial explanation of some phenomenon. An explanation of E by F is a full one if F includes both a cause, C, and a reason, R, which together necessitated the occurrence of E. (Recall that on the Hempelian account of scientific explanation C are initial conditions and R natural laws; whereas in personal explanation C is a person, and R that person's intentions, beliefs, and capacities.) If C and R together provide a full explanation of E, nothing else logically contingent beside C and R needed to be so in order for the occurrence of E to be guaranteed, and so a proposition reporting C and R entails a proposition reporting E. Thus a scientific explanation of an eclipse of the moon E is a full one if it cites all the natural laws involved, L (laws of motion and laws of light propagation), and precedent states of the world C necessary for the occurrence of E, viz. the positions and masses of moon, sun, and earth, and the absence of other heavenly bodies in the region, and if L and C together entail E. An explanation of E is only a partial one if the explanation includes factors which brought about the occurrence of E, but these factors did not necessitate the occurrence of E.
Now a full explanation really does by itself explain why something happened. It does so quite independently of whether or not there is an explanation of how any states it cites came to be (e.g. why the sun was where it was) or why any reasons which it cites operate (e.g. why certain natural laws hold). To suppose otherwise is to commit a fallacy which we may call 'the completist fallacy'. Clearly it is a fallacy. For if it were really the case that F could not explain E, unless there is an explanation of F, nothing in the universe could be explained, unless there were explanations of such things as the origin of our galaxy—which is absurd. It is however a fallacy commonly committed both by opponents and (as we shall see later) by supporters of natural theology. Thus Hume objects in the Dialogues to postulating a God who planned the world as an explanation of its order, on the grounds that the postulated existence of a rational agent who produces the order of the world would itself need explaining. Picturing such an agent as a mind, and a mind as an arrangement of ideas, Hume phrases the objection as follows: 'a mental world or Universe of ideas requires a cause as much as does a material world or Universe of objects.' Hume himself provides the obvious answer to this—that it is no objection to explaining E by F that we cannot explain F. But then he suggests that the F in this case, the mind, is just as mysterious as the ordered universe. Men never 'thought it satisfactory to explain a particular effect by a particular cause which was no more to be accounted for than the effect itself'. But that is plainly false. We can give a perfectly good explanation of how it came about that Jones lost his fortune in terms of the way the Monte Carlo roulette wheel spun, while being entirely unable to explain why the roulette wheel spun as it did, and indeed while judging that there was no explanation of how the roulette wheel spun, this being something utterly beyond accounting for. Nevertheless, although a full explanation of E (in the sense of 'full explanation' which I have delineated) leaves no facet of E unexplained, further explaining can often by done—there may be explanations of why the factors cited in the explanans are operative and how they came to exist. Let us concentrate for the moment on explanations of the operation of the factors at the time at which they bring about E. Let the factors be C, the cause which brings about E, and R, the reason for C's efficacy. Let C bring about E at the time t. The existence of C at t may depend on some other factor B which at time t makes C exist. Thus suppose my arm by moving makes to move the stick which I am holding, the motion of which moves a stone, and suppose that the transmission of motion is instantaneous; then the motion of the stone (E) is brought about by the motion of the stick (C) which in turn is brought about by the motion of my arm (B). Then the present existence of a cause is dependent on the present operation of its own cause. Likewise the operation of the reason R may depend on some higher-level reason S which at the time of R's operation makes R to operate. Thus Galileo's law of fall operates on earth because earth has such and such a mass and Newton's laws operate. I now define a complete explanation of the occurrence of E as follows. A complete explanation of the occurrence of E is a full explanation of its occurrence in which all the factors cited are such that there is no explanation (either full or partial) of their existence or operation in terms of factors operative at the time of their existence or operation. Thus suppose that a high tide is brought about by sun, moon, earth, water, etc. being in certain positions and by the operation of Newton's laws. Here is, let us suppose, a full explanation. Suppose too that Newton's laws operate here because this region of the universe is relatively empty of matter and Einstein's laws of General Relativity operate. These factors act contemporaneously to make Newton's laws operate. Suppose too that nothing at this instant makes sun, moon, etc. be where they are (even though some past cause was responsible for their being where they are). Nor does anything at this instant make Einstein's laws operate or this region of the universe be relatively empty. Then there is a complete explanation of the high tide in terms of the operation of Einstein's laws, the universe in this region being relatively empty of matter, and sun, moon, earth, water, etc. being where they are. Complete explanation is a special kind of full explanation. I now delineate as a special kind of complete explanation what I shall call ultimate explanation. To speak loosely to start with, we have an ultimate explanation of some phenomenon E if we can state not merely which factors C and R operated at the time to bring E about, and which contemporaneous factors made C and R exist and operate at that time, and so on until we reach factors for the contemporaneous existence and operation of which there is no explanation; but also state the factors which originally brought C and R about, and which factors originally brought those factors about, and so on until we reach factors for the existence and operation of which there is no explanation. Less loosely, I define an ultimate explanation of E as a complete explanation of E, in which the factors C and R cited are such that their existence and operation have no explanation either full or partial in terms of any other factors. Those factors are ultimate brute facts. Suppose that there is no God, that the universe began with a bang in a state X at a time t, that it is governed by deterministic laws L (whose operation is not further explicable); and that in accord with L, X brought about a state Y, and Y brought about a state Z, and Z brought about E. Then (X and L); and (Y and L), and (Z and L) are each complete explanations of E; but only (X and L) is an ultimate explanation of E. Finally let us delineate as a special kind of ultimate explanation, what I shall call absolute explanation. An absolute explanation of E is an ultimate explanation of E in which the existence and operation of each of the factors cited is either self-explanatory or logically necessary. Other explanations cite brute facts which form the starting-points of explanations; there are no brute facts in absolute explanations—here everything really is explained. I do not believe that there can be any absolute explanations of logically contingent phenomena. For surely never does anything explain itself. P's existence at t 2 may be explained in part by P's existence at t 1. But P's existence at t 1 could not explain P's existence at t 1. P's existence at t 1 might be the ultimate brute fact about the universe, but it would not explain itself. Nor can anything logically necessary provide any explanation of anything logically contingent. For a full explanation is, we have seen, such that the explanandum (i.e. the phenomenon requiring explanation) is deducible from it. But you cannot deduce anything logically contingent from anything logically necessary. And a partial explanation is in terms of something which in the context made the occurrence of the explanandum probable, without which things would probably have gone some other (logically possible) way. Yet a world in which some logically necessary truth did not hold is an incoherent supposition, not one in which things would probably have gone some other way. These are among many reasons why it must be held that God is a logically contingent being, although maybe one necessary in other ways. So for these reasons let us leave aside consideration of absolute explanation, and return to explanations of other types. I suggest that the arguments to the existence of God with which we are concerned are arguments to a complete explanation of phenomena, but not necessarily arguments to an ultimate explanation. They all claim that God's present action (which has no explanation in terms of any other present factor) brings about certain present phenomena, while not necessarily denying that there may be partial past causes of that action—viz. God's own action in the past in keeping himself in existence may have helped to make possible his present action. The issue turns on just how temporal a being the theist claims his God to be. He may regard him as a being who keeps himself in existence the following moment by his own choice at each moment of time. Or, more traditionally he may regard him as a being who is in some sense necessarily eternal. In the latter case if he exists at any time, then necessarily he exists at all times. In that case any complete explanation of any phenomena in terms of God's action at a certain time would also be an ultimate explanation. For the explanation is in terms of God's existence and his intention. His intention has no explanation; he freely chose to act on that intention at that time; and his existence at the time would not be explicable in terms of anything earlier or contemporaneous, and so not explicable at all. Whereas if God is the cause of his own subsequent existence, his existence at a certain time, which forms part of a complete explanation of some phenomena, would be explicable further. At this stage I allow the possibility that arguments to God's creative action provide only complete, but not ultimate explanations of phenomena. However, in the next chapter I shall be producing arguments in favour of God's being a necessarily eternal being. For this reason I shall confine myself to examining our grounds for supposing that we have reached a complete explanation of phenomena. However, if God is a necessarily eternal being any complete explanation in terms of his action will also be an ultimate explanation.
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