fear of such things as cats, mice, caterpillars, and common snakes, which they know perfectly well to be harmless. Thus the alleged explanation is too simple; for it ignores an important part of the facts to be explained. .

The second danger is that of attaining simplicity in explanation by ignoring the relations of the facts we are trying to explain to the rest of the world. The ideal of all science and philosophy is the simplest possible connected view of the whole universe; but in trying to attain it we must not be penny wise and pound foolish. There is a difference, as Kipling says, between a team of good players and a good team of players; and there is a difference between a set of good explanations and a good set of explanations. A simple explanation of some one little fact that will not fit in with our explanations of the rest of the world is not so satisfactory as a more complicated explanation that will. Suppose, for example, that the old witchcraft and demonology or that the modern telepathy and spiritualism gave or could be made to give a perfectly simple, coherent, and well-articulated explanation of the particular set of facts with which they deal. The explanation given would be extremely unsatisfactory, and would doubtless be rejected by many scientists as wholly unscientific, so long as there was no way of fitting the telepathic and spiritualistic conception of things in with the vast and evergrowing mass of facts that are being continually explained and coördinated more and more closely every day from other points of view. If the facts that the telepathists and spiritualists deal with can be explained piecemeal by principles recognized elsewhere, no scientist doubts that such an explanation is far better than one by thought-transference and spirits, although the latter might be a great deal simpler so far as the one set of facts was concerned.

It was some such feeling as this of opposition to the introduction of totally new principles of explanation serviceable in only one special field that Newton expressed in his celebrated dictum Hypotheses non fingo. The cause which we assign

for any known effect must be, he said, vera causa: a true cause, or one for whose existence we have more evidence than can be found in the special facts that it is invoked to explain.

A third danger connected with the principle of simplicity is the opposite of that just explained. It is undoubtedly true that a complicated explanation of the facts in some one field, that fits in with what we know about all the rest of the world, is better than a simple explanation that does not, and it is just as true that we must not accept the new set of causes until we have made a reasonable effort to explain the various facts in question by old ones; and yet, on the other hand, we must not carry our rejection of strange causes to an extreme. If the alleged new principle does nothing else, it may serve to hold together a mass of facts many of which would otherwise escape us or become hopelessly confused, and to keep us puzzled until we find some other explanation that is better. In this way even a false hypothesis is often better than none at all. And then, again, it may turn out that our disconnected principle is not false after all. It is true that our scientific ideal is a simple, well-coördinated view of the world as a whole; but it is also true that we are a long way from attaining it. What we possess in the way of knowledge is not so much one field that is always growing broader as a large number of fields each of which is growing out towards the others so that sometimes they meet; but there are still plenty of gaps, and we must not always refuse to cultivate some new field because we do not see how it can be joined with the rest. It is nearly as ent hypotheses consistent with each other too soon as not to try to do so at all. The Greek philosophers except Aristotle were always thinking about the sum-total of things, and Aristotle is the only one of them who made anything like a respectable contribution to science. Descartes was thinking about the ultimate relations of mind and matter, and his general standpoint compelled him to say that the lower animals were mere automata: mechanical toys that cried when you

bad to try to make our differ

kicked them, just as a bell rings when you shake it, without any feeling whatever.

Thus the Principle of Simplicity or Parsimony is one that we are compelled to follow, but often it is hard to tell whether we will not reach it sooner in the end by leaving it for the moment.

The right to assume these

principles.

Of course it is one thing to be so organized that the simple and familiar are more easily believed in than the complicated and unfamiliar, and a somewhat different thing to accept the formal principle that where there are two theories, equally good in other respects, that which assumes the simpler and more familiar state of affairs is the more likely to be true. And yet if we have the organization, we can hardly avoid the principle. To say that the simpler and more familiar is more easily believed in means that in most cases we do believe in it, or, in other words, that in most cases the relatively simple and familiar state of affairs is what we call the 'true' one; and now, a large number of particular cases being settled, all we have to do is to compare them and we reach our formal principle: The theory which supposes the simpler and more familiar state of affairs is more often true than the other.*

It is because we act on this principle of discrediting the new, whether we ever state it in words or not, that the phrase a very strange story' generally means a lie.

So much for the fact that we actually do use Consistency, Conceivability, and Uniformity and Simplicity as tests of truth, and even for the further fact that we come to think we have a right to. But have we this right? Is it possible to prove that there is such a relation in the world as com

*We get the principle when we reflect enough to see the results of our own organization (i.e., to see that all our explanations are relatively simple) but not enough to see that they are the results of that organization (i.e., that these explanations are simple because the simple ones are those we chose). When we see that the question takes a new form.

patibility or incompatibility? Can we prove that anything real conforms or ought to conform to the laws of our imagination? Hardest of all, can we prove that because something is uniform or simple and therefore easy for us to think of, it is any easier on that account for it to exist? And if we cannot prove these things, have we any real right to use the tests? My answer so far as uniformity is concerned has been given already in Chapter XXII. I believe that we cannot prove these things, and therefore cannot prove our right to use the tests. We simply take them for granted and take the right to use the tests for granted along with them.

The time has gone by long since when wise men sought for a philosophy without assumptions; and if we cannot get along without them in philosophy, we certainly cannot get along without them in common life and in the logic that tries to serve as a guide for common life. If any one believes, as Kant did, that not only colors and sounds and smells and tastes, but also Space and Time with all their relations of shape, size, distance, direction, duration, coexistence, and succession, are purely human ways of imagining things and do not really belong to things in themselves at all, then that person ought not to use conceivability as a test of what things in themselves can or cannot be. If any one has meditated about these topics so long that it no longer seems to him absurd to doubt the simplicity and general rationality of Nature, I do not see how it is possible to restore his faith by demonstration; and if he has emancipated himself from the bonds of habit so completely that he really doubts the existence of those principles of uniformity that we indicate by the words Thing and Kind and Cause and Law, then there is certainly no way of proving to him that one explanation is better than another, or indeed that anything needs explanation at all. If, finally, he really and truly doubts-as Descartes tried to the existence of everything but his own passing thought, I do not see how we could prove to his satisfaction that there is a real nature of things in virtue of

which one supposed fact is incompatible with another, and therefore that there really is such a thing as a contradiction.

If people actually doubt all these things, we do not argue with them we lock them up instead, and by this resort to brute force we confess defeat in the field of pure argument. If, on the other hand, they profess to doubt them, but show by their acts or their argument—perhaps by the very fact of talking with us that when they are off their guard they really take them for granted, the most we can do is to point out the inconsistency, with the hope that their faith in law and a nature of things is so strong at bottom that inconsistency in an argument will seem to them a fault. We cannot go beyond this appeal to faith. Thus we start with faith in experience as a whole, however vaguely we may conceive of this experience; but such a faith implies also faith in all the ultimate principles that that experience involves.

There are some questions which logic and its tests of truth will never help us to settle. If it is a question whether a certain state of affairs exists, and if there is no objection so far as consistency and conceivability of proof. are concerned to believing that it does, the only

The limits

way of settling the question is to ask whether any one has observed the state of affairs itself or anything that can be recognized as its necessary cause or effect. If we cannɔt observe the state of affairs itself and if we cannot prove that anything which we do observe must be connected causally with something of the sort, we cannot prove that it exists. But if the state of affairs in question is one that might exist without being observed or producing unmistakable effects, we cannot prove either that it does not exist. It may be that

there are mountains on the other side of the moon; but we cannot see them, and we do not know of any change that they would make in what we do see if they were there; consequently we cannot tell whether they are there or not. It may be that plants feel, that they enjoy the sunlight and the rain and suffer discomfort in the cold; but feelings can