SO much for the relation between mind and body. The relation between life and body is also a subject for discussion between the two schools. Some, though not all, dualists assert that life, like mind, has an existence distinct from that of the body and that it controls the structure and behaviour of living substance. Just as in their view lifeless mechanisms result from the action of a non-material mind on matter so, they say, all living organisms result from the action of a non-material influence called life on matter. In the terminology that I have introduced in Chapter IV all such mechanisms are diathemes. According to dualism machines are diathemes because they result only when, with the help of the hands of those who invent and construct them, non-material minds act on the substances of which they are made. Machines are thus regarded as doubly determinate, as determined partly by the action of physical forces and partly by that of minds on matter. Living organisms are similarly regarded as doubly determinate, as determined partly by the action of physical forces and partly by that of life on matter.

Monists, of course, deny all this. In their view the word diatheme does not represent any reality. All structures are adiathetous. Mechanisms, be they living or lifeless, cannot be distinguished in any significant way from random collections of objects or particles. Hence it is relevant to ask:

Is there a criterion by which to distinguish between a diatheme and an adiathetous structure?

As the monist denies that the distinction exists he will answer "no". And if no criterion can be found his case will be strengthened. Conversely the case for dualism will be strengthened if there is such a criterion. For the dualist asserts that all mechanisms, be they living or lifeless, together with all other things that require some mental activity for their production, belong to a class of object significantly distinct from all things that come into existence without the agency of mind or life. This particular question has been very fully discussed in Science versus Materialism, and so there will be no need to add much to it here. But mere mention of the question makes it evident how very irrelevant the following one is:

Is there a criterion by which to distinguish between living and lifeless mechanisms?

I do not say that this question is not interesting and important. There is much to be said about it. It is relevant to many problems. But a decision between monism and dualism does not depend on the answer. The monist would say "not a decisive distinction", because he believes that both are the result of the unaided action of matter on matter. And the dualist would also say "not a decisive distinction" because he believes that both are the combined result of the action of physical forces on matter and of other causes with a non-physical origin. Nevertheless both might well agree that a distinction of some kind can be made. In short if adherents of both schools thought the question out, they would find that it does not divide them; it is one on which they can agree. Yet materialists of various schools have told me over and over again that they base their conclusion that dualism is wrong on the difficulty of finding a reliable criterion by which to distinguish between living and lifeless mechanisms. In particular the present uncertainty as to whether viruses are alive or not has recently been hailed as a strong argument against the view that living substance is partly controlled by non-material influences.

Relevant to the question whether the term diatheme has any real significance is this:

In the production and behaviour of the structures called diathemes can one observe the operation of any principle not seen to operate in the production and behaviour of adiathetous structures?

Proof of such a principle would support dualism for it would show that diathemes are doubly determinate. And proof that there was no such distinguishing principle would show that the things referred to as diathemes were really not essentially different from those referred to as adiathetous structures. Such a proof would show that all objects are singly determinate and would justify monism. This particular question too has been very fully discussed in Science versus Materialism. I do not propose to add much to it here. But again its mere mention shows how irrelevant it is to ask

...Do all processes in the organic world conform to the laws of physics and chemistry?

The question is irrelevant because both monists and dualists must believe that they do. And no one who understands the question could doubt that they do. The answer "yes" does not depend on observation and experiment; it is true by definition. As I have emphasised in Chapter I, no one could deny that some of the component causes of every event in living substance are physical forces. For to say that substances are material is to say that the interaction between them is effected by the operation of physical forces. And to say this is to say that the substances conform to the laws of physics and chemistry; for these laws merely define the interaction of physical forces. Where there is matter there must be the laws that characterise matter and these laws must be observable on every occasion when matter acts on matter. The dualist does not doubt that the ink flows from the poet's pen in conformity with the laws that characterise the behaviour of ink. To assert that production of the poem is an event in which a non-material mind plays a part is not to deny that those material substances that also play a part are material substances and behave as such. If it is said that a thing without location (such as the poet's mind) acts, though it be indirectly, on a thing with location (such as ink) it is, nevertheless, implied that the ink behaves like ink. And if it is said that a thing without location acts on myosin in the poet's muscles, it is equally implied that the myosin behaves as chemists know myosin to behave. If it did not the conclusion would not be that a law of chemistry was being broken. It would be that the substance was not myosin after all. The relevant question about laws is:

Are the laws of the physical sciences the only ones to which living substance conforms or can one observe in such substance the operation of two sets of laws, the operation firstly of those of the physical sciences and secondly of another set that has no place in the physical sciences?

To prove that there is only one set of laws would be to prove single determinateness and thus to justify monism. To prove that a second set operates (additional to the first set, not in substitution for it) would be to prove double determinateness and to justify dualism. Which is right depends on whether the laws of biology are deduceable from the laws of physics. Many have said that they are. But this opinion is no more than a declaration of faith. And those who make the declaration are more often biologists than physicists. The latter will, I think, feel less sure about it. The prospect of deducing from the laws of physics the biological law, for instance, that a chicken must hatch out from a hen's egg, must seem to a physicist rather slender. Monists must at present at least be satisfied with the fact only that the production of the chicken is not inconsistent with physical laws. But I have just explained that this is not the same thing as to say that it is deducible from physical laws. To show that, in the production of the chicken, physical laws operate proves nothing.

An allied irrelevant question is this:

Are any events in the organic world indeterminate?

As monists say that these events are fully determined by the laws of physics and chemistry the answer "no" is welcome to them. And as dualists say that these events are more determinate than if they were determined only by the laws of physics and chemistry the answer "no" is just as welcome to them too. And yet both sides are wont to argue heatedly for and against a theory of indeterminateness as though a decision between the two schools depended on it. The discussion is, let me repeat, mightily confused.

Lastly, a relevant question that I have not seen raised anywhere but that may prove the decisive one:

Can one localise any events in living substance and prove them to be incompletely caused by all the physical forces that contribute to them?

If the answer is "no" it supports monism and if it is "yes" it supports dualism. For the answer "yes" would mean that some of the causes of the event were other than physical forces and were, therefore, attributable to a non-material influence, to a diathete. But I can hardly expect the question to convey much when it is stated thus tersely and without context. I can hardly expect even that it will seem worthy of further attention. Its significance can only be appreciated after a sustained argument and this will be presented in the second and third parts of this book.

Let me now summarise the conclusions that have emerged from this discussion of relevant questions. When scientific method is applied to all relevant questions a baffling conflict of evidence is found. On the one hand it seems to be proved scientifically impossible for a thing that lacks location to act on a thing that has location; but on the other hand the evidence is very conclusive that this happens. Hence the great problem. It is to reconcile the apparent proof that double determinateness is impossible with the apparent proof that it occurs. I shall call it the Problem of Interaction. It seems to be one of the biggest with which science has ever been challenged.

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