Can we in any better way reconcile desire and fate? In the belief of the scientist the future can yield to an objective analysis only if he can put aside all desire of one future or another; and yet, in reaching for this unattainable understanding, by some mutual influence his desires and the events may grow more and more into harmony. Holding this hope, or better still, moved by a pure curiosity for things to come, how is it possible to examine scientifically the future? For in the science of the future observation is as impossible as experiment; and of the three methods there is left to us only prediction. In the other sciences prediction plays but a small part, and rightly so, for verification follows closely on its heels; but there are general methods in scientific prediction and we may try to apply them in dealing with the whole future state.
First and always, it is necessary to exclude as far as possible, illusion; for to most of us the future is the compensation and fulfilment of all that the present and the past have lacked; and the future being unknown and incontrovertible has been a fair ground on which to place all these hopes and desires. But in scientific prediction these desires are the most delusive guides. The opposite danger is as great and more insidious: in our lives we take the present for granted to an extend far greater than we can realize, so that even when we are thinking of the future we cannot separate the historic accidents of the society in which we were born from the axiomatic bases of the universe. Until the last few centuries this inability to see the future except as a continuation of the present prevented any but mystical anticipations of it. Luckily these complementary errors affect different parts of the future. It is in the near future where we are still sympathetically related to men and events that our desires have the most power to twist our appreciation of facts. We care less about the more distant future, but to approach it at all we must divest ourselves of so many customary forms, that even the more enlightened prophets lets their imagination stop in some static Utopia in despite of all evidence pointing to ever increasing acceleration of change.
What positive ideas can be found to take the place of the naïve anticipation that the future will be like the present but more pleasant (or more unpleasant according to one's disposition)? The leading principle is that by which Lyell founded scientific geology: the state of the present and the forces operating in it contain implicitly the future state and point the way to its interpretation. We have three disciplines of thought to help us to this interpretation. History (of which human history is only a minimal part) tells us how things have changed and how by inference they will change in the future. Strictly, prophecy should be treated as part of history, but, until history has found its laws, it must chiefly be used as a storehouse of illustrative facts; though one might say loosely that everything that will happen must conform with the spirit of History. The physical sciences, as far as we know them, give us the material of which future as much as past is built, and the manner of that building. The manner appears to us as physical law but it may well be found to be a tautology which we are congenitally too limited to grasp. Lastly there is the knowledge of our desires, but though the future according to our desires, is an illusion, our desire are, paradoxically, already tending to be the chief agent of change in the universe; it is only that the actual change is so rarely the desired change.
The initial difficulty in the general prediction of the future is its enormous complexity and the interdependence of all its parts; but this complexity is not completely chaotic and we can always attack it by considering it as a product of chance and determinism, chance where we cannot see relationships, determinism where we can. The events out of which so complicated a thing as the general state of the universe is built, form neither one indivisible whole nor a set of equally independent units, but consist of complexes (nebula, planet, sea, animal, society) of which the components are themselves complex parts. This hierarchy of complexes is not imagined to have any objective validity, it is only an expression of the modes of human thought, a convenient simplification which makes science possible. Inside each complex, development proceeds according to its own rules, determined by the nature of the complex; but these rules always include, if they do not entirely reduce to, what is, in effect, the statistical chance interaction of complexes of a lower order. The death-rate of a town, for instance, can be shown to be a function of the amount of money it spends on sanitary measures, but the individual deaths appear, from the point of view of the town, to be due to chance circumstances, though again for each individual concerned they are determined. We can always leave out the higher complexes when we are considering the lower. An atom of oxygen will respond to its environment in the same way in a nebula, in a rock, or in a human brain.
Now the complex we are concerned with here is the human mind, and so we can fairly start with the assumption that the rest of the universe goes on its way determined by its physical, chemical and biological laws except in so far as man himself intervenes. Absolutely, we know hardly anything of these laws, but relatively to our knowledge of human behavior we know them so well that the future they present - the astronomical, geological, biological future - seems a fixed and stable thing.
In human affairs the immediate future reveals itself in the following of tendencies visible in the present; beyond that must come the application and development of present knowledge. This is the minimal basis for prediction; but our present knowledge carries with it the implication of still further advances in knowledge along the same lines. It is the applications of this new knowledge and the secondary results that flow from them that will chiefly concern us, because it is clearly impossible to go further and include unimagined discovery. Of course, there is a considerable chance that one of the unpredictable discoveries will be so important that it will turn aside the whole course of development. But to be deterred by this chance would be to abandon any attempt at prediction. Already the chance element comes in when we consider applications or developments of knowledge in more than one restricted field; because although we can predict the development in that field fairly well, we cannot predict the rate of development; and so the rates of development in different fields, which are constantly reacting on each other, being unpredictable, the resultant future becomes more and more uncertain the father we look forward. The only way to deal with this complexity is by separating the variables as best we can, by arbitrarily considering developments as proceeding in one field without any developments in any of the others, and then combining the results attained by applying this method in different fields. At the same time we must keep in mind that the state of development at any one time period must be a self-consistent whole. Each line of development must have reached the level which is implied by the necessities of any of the other lines: for instance, the chemical control of life requires the development of chemical technique and apparatus of a very high order. On the other hand, whole sections of certain developments may become superfluous owing to developments in other fields; for instance, the manufacture of synthetic food and the industry connected with it would be unnecessary if blood were used directly as the motive power for animals.
Obviously we cannot proceed with this method in detail: if we could, we should not only be able to predict the future exactly, but to make it the present. For brevity, it is worth considering three fields only.
Man is occupied and has been persistently occupied since his separate evolution, with three kinds of struggle: first with the massive, unintelligent forces of nature, heat and cold, winds, rivers, matter and energy; secondly, with the things closer to him, animals and plants, his own body, its health and disease; and lastly, with his desires and fears, his imaginations and stupidities. In each of these divisions in turn we will make the arbitrary assumption that his progress in it will continue while in other respects he remains the same.