THERE remains one further argument against vitalism which we believe is to many materialists far more cogent than any of those which we have just been reviewing. We have not found mention of this argument in the writings of any biologist-philosopher, which is perhaps natural. For it does not depend on what men know about biology but on what they think they know about physics.

The argument is this. The Material Universe is completely determinate. Consequently the laws of physics and chemistry permit no latitude whatever to the course of events; consequently the laws of evolution, and the laws of behaviour, and the laws of physiology must all be really laws of physics and chemistry, whether they look like it or not; consequently it is impossible for non-material influences to interact with Matter. If there were any such influences they could not possibly have any effect on the course of material events. So all the manifestations commonly attributed to God, the Soul, Mind or Life, can, in fact, only be due to the unaided action of Matter on Matter.

Those who believe in the complete determinateness of the Material Universe ought to reply to philosopher, theologian, vitalist, to everyone who believes in non-material reality with the above few sentences. For it is impossible to believe in a non-material God, or that Mind, Life or the Souls of men are non-material if one is convinced that the Material Universe is a self-contained system incapable of interacting with any non-material influences. The theologian must give up his theology if he is not prepared to admit some gap in the complete determinateness of the Material Universe.

Most, if not all materialists do believe in such complete determinateness. They go so far as to tell the world that science proves it. We suspect that this is the only true reason why they are materialists. Yet they do not state this reason in its clear and obvious terms. If they did they would have no need to write whole books to prove that vitalism is dead. All they had to say would be contained in a single paragraph. But they treat the simple and direct line of argument which is ready to their hand like a stinging nettle to be touched gingerly or avoided altogether and prefer to justify their faith with recondite biological researches of which we, with the best will in the world, cannot discover the relevance.

It becomes our duty to clasp the nettle firmly, for we cannot know whether it is worth while to continue our investigation until we have considered whether belief in the complete determinateness of the Material Universe is fact or fancy.
Does physics contain a Principle of Complete Determinateness?

Common Sense takes it for granted and common experience seems to justify such an impression. It has, indeed, become one of the tribal behefs of the Western nations. But what does science say?

The answer is: "Nothing." Most physicists tend to believe in a Principle of Complete Determinateness. But they would be the first to admit that their behef is based on faith and not on fact. Many laws and principles are known to science. There are the first and second Laws of Thermodynamics, the Principle of Conservation of Momentum, the Laws of Gravitation and Motion, the Principle of Least Action, the Restricted and General Theories of Relativity. But there has been no discovery of a Principle of Complete Determinateness. There is no authority whatever for the assumption of such a Principle. There is no experiment or observation, or piece of deductive reasoning to prove it. All that can be said is that its assumption has become so ingrained in our habits of thought that few persons are prepared to give it up readily. Yet this assumption must be tested like any other of those adopted by Common Sense.

We are certain that physical events are not completely indeterminate. For when we repeat an experiment under circumstances which are, so far as we can verify them, identical, the results are, so far as we can verify them, identical. The words in italics are important. They emphasize that, while physical events are almost completely determinate, we cannot prove that they are absolutely so. Perhaps, with more accurate means of observation we should no longer find that identical conditions led to identical results. Only if we could achieve absolute accuracy could we know with certainty. And absolute accuracy is impossible.

This was always known. No one ever denied that some small errors are inevitable in every observation, and scientists are in the habit of stating the probable error in their records. But so long as the improvement in accuracy kept pace with practical requirements any inevitable small errors had no effect on scientific conclusions. Investigators could afford to treat them as negligible.

Only when physicists turned their scrutiny on the very fine structure of Matter and Space did the attainable limits of accuracy demand renewed attention. This led to the enunciation of Heisenberg's Principle of Indeterminacy. In spite of its name this principle does not assert that any events are indeterminate. In one of its formulations it asserts that both the velocity and position of a particle cannot be simultaneously ascertained with absolute precision. This is, however, only one of many possible ways of expressing a general principle concerning measurements in physics. Such special application of the principle need not concern us here. It may suffice for us to note that Heisenberg has formulated clearly the theoretical limit of accuracy for any observation and has stated the reason for it. It is the limit which cannot be passed even with the most perfect apparatus and technique.

By drawing attention in this way to the fact that some of the data concerning the behaviour of Matter cannot be observed with absolute accuracy, Heisenberg's Principle has led physicists to reconsider the scope of causality. Having, for the first time. occasion to think about the matter, they have not been slow in pointing out that the inevitable small errors of observation may mask some small degree of indeterminateness.

It is a long step from the admission that complete determinateness cannot be proved to the assumption that there is no such thing. So we should require better reasons than the well-known fact that all observations are a little inaccurate for throwing over a Principle of Complete Determinateness in favour of a Principle of Incomplete Determinateness. Both are hypotheses. Where two hypotheses are available, both equally unproven, we apply the Principle of Economy of Hypotheses and adopt the one involving the lesser assumption provisionally. But which here does so ?

We might consider that the Principle of Complete Determinateness requires the lesser assumption because it is the one most compatible with Common Sense. But this principle attributes something absolute to Nature, something we should have to describe as perfection. We might equally well consider that the minimum assumption is to attribute to Nature some slight departure from perfection. Because of this uncertainty some physicists prefer to believe in a Principle of Complete Determinateness, others in a Principle of Incomplete Determinateness. A study of the inorganic world does not and probably never will prove which is right.

But to secrets which the inorganic world jealously guards the organic world may provide a key, and it seems strange indeed that physicists have never thought of drawing conclusions from a study of Matter during its passage through a living organism. For at such times Matter exists in a peculiar state not reproducible elsewhere and the physicist has always been rewarded when he has studied Matter under new conditions.

Research has, in the past, been particularly profitable when the conditions have been extreme. Physicists have learned much from observing what happens at very low temperatures in the neighbourhood of the absolute zero, and at very high temperatures such as occur in stars, and when substances are very tenuous as in a vacuum tube, and when they are very dense as in the white dwarf stars, and in intense electric and magnetic fields, and when particles move with velocities approaching the limit of possibihty, namely the velocity of light.

During its passage through a living organism Matter is not subjected to any of these extremes. But it is subjected to another extreme never found outside an organism. This is an extreme of unstable equihbrium. Particles are sometimes so delicately poised that their position depends on a balance of forces far closer than can ever be obtained in the inorganic world. Maybe the conditions for equilibrium in certain organic substances would provide the physicist with a scale of measurement which would enable him to reach closer limits even than the close ones set in the inorganic world by Heisenberg's principle.

We offer the suggestion for what it is worth and shall have a little more to say about it on some other occasion. At present we are only concerned to note that to base materialism on the assumption of a Principle of Complete Determinateness is to base it on a hypothesis for which there is not one scrap of evidence. To base vitalism on the assumption of a Principle of Incomplete Determinateness would be equally unsound. The choice between materialism and vitalism does not depend on evidence for or against either principle. It is the other way about. The choice between the two principles depends on the evidence for or against vitalism.

Of course it might be objected that, for all practical purposes, almost complete determinateness is as good as quite complete determinateness. We know from experience that, if there be a gap in the complete determinateness of inorganic events, it must be a very narrow gap indeed. We have said above that, when we repeat an experiment under circumstances which are, so far as we can verify them, identical, the results are, so far as we can verify them, identical. And physicists can verify the conditions and results very closely. Methods of measurement are so accurate that the quantum of action has been determined with precision. It is 6.55 x 10^-27 erg seconds. An erg is very roughly the amount of energy expended by a fly when it crawls one-third of an inch up the window-pane. So hundreds of millions, of millions, of millions, of millions (yes, millions must be said four times) of measurable units of action make up an amount which we should still regard as small. Yet any uncertainty in a scientist's ability to verify identical conditions must concern measurements of at least the same order of magnitude as that of the quantum of action. In Philosophy and the Physicists, Professor Stebbing has rightly referred on page 214. to "the ridiculously small amount of indeterminacy that the measure of the uncertainty relation involves". From this it has been argued that indeterminateness, if it exists at all, is only in microscopic, or rather in sub-microscopic bodies, and that a living organism, being a macroscopic body, can only show a negligible amount of physical indeterminateness.

A reader who believes this will be convinced that, if not quite determinate, the Material Universe is anyhow sufficiently determinate to render effective interaction between non-material influences and Matter impossible. Handicapped by such a preconception he will not be as receptive as we should wish for the evidence for such interaction which we propose to bring. It therefore becomes a part of our task of clearing the ground to point out that almost complete determinateness is not as good as quite complete determinateness. An indefinitely small latitude in the behaviour of Matter under the influence of physical forces would be enough to enable non-material influences to affect the large-scale course of events.

Engineers are familiar with methods for magnifying small effects. Heavy machinery can be controlled by little push-buttons. A faint disturbance in the ether due to a wireless signal sent out in the U.S.A. can be brought to bear on a series of relays and made to produce a loud noise in millions of English homes. Trifling differences in the colour of biscuits can be distinguished by photo-electric means with the result that tons of biscuits may be separated by an automatic sorting machine, the saleable ones being packed into boxes and the inferior ones rejected. Pascal has said wittily that a small difference in the length of Cleopatra's nose would have altered the whole course of history.

An indefinitely small latitude can always be enlarged to any extent by summation or multiplication when a principle of discrimination is introduced, as every physicist knows. Clark Maxwell pointed out that a discriminating demon could produce a large difference in temperature between two vessels containing a gas if he were allowed to open a tiny aperture between them whenever a fast molecule approached the apparatus in the direction from vessel A to vessel B, and whenever a slow one approached in the opposite direction. In time, A would contain only molecules moving with a high velocity and contain gas at a high temperature while B, with low velocity molecules, would be cold.

In particular do "great effects from little causes spring" when a system is very delicately poised. Living substance is in this condition and we have no knowledge yet of the degree of unstable equilibrium in the most vital tissues. No means of observation has yet been devised delicate enough not to upset the balance and, thereby, spoil the investigation. All we do know is that the conditions are such that a Clark Maxwell demon (another name for non-material influence) would not require much latitude to enable him to produce a conspicuous effect. The instability and complexity of some organic molecules may well be such that the demon could introduce large-scale disturbances even though he operated on a scale greatly below that given by atomic dimensions.

We have, therefore, no right to reject vitalism, or religious belief, or any other form of idealism merely on the grounds that there is not enough latitude in the behaviour of Matter to allow non-material influences to be effective. If we find, after studying the nature of the organic world that such influences are effective we shall know that there is a gap in the determinateness of the Material Universe, though it be but a very narrow gap indeed. As a side line our work will then have presented physics with a new principle, a Principle of Incomplete Determinateness and thus have settled a controversy which, we believe, cannot be settled in any other way.

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