A RELAY is, as I have pointed out already, irreversible. Diathesis can pass through it in one direction and not in the other. As a path for diathesis consists of relays in cascade the whole path is also irreversible. Which is only another way of saying that in our foundry the switches that enable the craneman to control the casting do not enable the casting to control the craneman.

This irreversibility enables one to speak of a path for diathesis. The relay to be found at the end might be called the last relay and the one at the beginning the first relay. For a reason that will appear in a moment I propose also to call the first one a primary relay. The others might then be called intermediate relays.

If one asks how the last or any intermediate relay is controlled the answer is simple enough. It is controlled by the relay one stage nearer to the beginning of the path. The contactors are controlled by the switches in the crane cabin, these switches by the craneman's muscles, his muscles by endplates, these by his nerves, and so forth. And somewhere near the beginning of any path one can say, in more general terms that relay number 4 is controlled by relay number 3; relay number 3 by relay number 2; relay number 2 by relay number 1.

And there the recital must end. If one asks by what relay number one is controlled the answer cannot be by another relay. For there is none. A primary relay is controlled, certainly. But it must be done by means that differ in principle from the means by which every other relay in the set is controlled. It is this difference that justifies the name of primary relay. How and by what is a primary relay controlled.

The question is, surely, very relevant, very important in science. Some scientists will, I am hoping, find in it a stimulating challenge. And yet. The question is disconcerting. I can well believe that some will find it irksome. Not that it is unreasonable. Anyone who says that a particular device is controlled by some other device must expect the question by what is that other device controlled. One of the things that makes the question disconcerting is that its logic is too simple to be easily ignored. One would like to be able to say that, hidden somewhere among the tissues of the brain, there must be a further device in control of the one that I have called a primary relay. And this easy way out is so obviously barred by the definition of a primary relay. As soon as one says that there must be a further device one realises that, if there were, this would be the primary relay and the question would remain as before, unanswered.

The truth is that the question what controls a primary relay is off all the traditional paths of scientific enquiry. And so the traditional methods by which scientists have successfully tackled their problems do not promise much help here. And the solution when it comes is not likely to fit readily into the existing body of accumulated scientific knowledge. It may shake some traditional notions that have come to be regarded as firmly established. Those who realise this may well hope that the question will soon come to be ignored and forgotten. They may well attempt to discourage those who would take it seriously. And if they cannot dismiss it they may well clutch eagerly and uncritically at the first facile answer that presents itself. It is one of the weaknesses of human nature (as is proved time and time again by political, religious, philosophical, and sometimes even scientific controversy) to prefer an unsound solution of a problem, provided only that it be comforting, to a sound one that is disturbing. An imp of complacency dwells in every one of us and urges us to dodge awkward questions. He will certainly urge us to stop asking what controls a primary relay.

Here are some of the things that the imp may whisper in our ears:

"This is not a real question at all. It has been artificially manufactured out of the words that have been used to form it. It melts away under the fierce light of logical scrutiny."

"The time is not yet for such a question. Let scientists first find out more about the working of the brain. When they have observed a primary relay they will see how it works. Then they will know what controls it and how the control is effected." (But, let me repeat, they will not observe what controls it. For if they did, the thing observed would, in turn, become the primary relay.) "The question is really quite simple. It has been answered by scientists and they have since proceeded to more important things."

"There is no such thing as a primary relay. Processes in the brain are controlled by the sense data received as stimuli from the outer world. Hence the series of relays does not have its beginning in the brain. It only passes through that organ. The series is infinitely long."

Whether such arguments will be regarded as foolish or plausible I do not know. They are certainly not too foolish to have found spokesmen among scientists of repute, as I have found both from my reading and from conversation. So the unsoundness of the arguments is evidently not immediately apparent. It is only exposed after a critical examination. I am obliged to consider quite seriously at least the argument that the question is not real and the argument that there is no device to which the term primary relay could apply.

Those who may think that the question has been artificially manufactured from the words in which it is presented could clairn (and no doubt with some justification) that I ought to have expressed my meaning differently. Some might object to my choice of the word "diathesis". They might prefer a longer word. Or alternatively they might prefer a shorter one, such as "control". Some might object to my way of speaking of diathesis as though it flowed from one place to another. (And it is worth noting here that it is equally possible to object to speaking of energy in that way.) Some might think that the definition is too inclusive. Others that it is not inclusive enough. And then one might argue with some reason that such devices as contactors, switches, muscle fibres, nerves, synapses ought not to be called relays. Neither engineers nor physiologists apply the word to any of these particular devices. Indeed a physiologist would describe the whole process by which the system of voluntary muscles is controlled in different terms from those that I have used. Having been reminded of all this by the imp of complacency one might be tempted to forget the irksome question about the control of a primary relay.

However, it is facts that matter and not words. Be it admitted that I could have pursued my investigation along a more traditional path, that I could have found a neater, clearer, more cogent formulation of the question. That would not prove that the question itself does not exist. What must be remembered is that the question would have presented itself in different words if I had approached it differently; but it would liave presented itself.

For it is a fact that a series of material devices is situated between the craneman's brain and the casting. It is a fact that these devices are so arranged that each touches off the next one in the series when it operates. It is, therefore, also a fact that they are all touched off in succession when the very first one operates. Whether this first one be called a primary relay or by any other name it remains true that it is the first of a series. This first device is touched off at the required moment and only at that moment. So it is controlled. By what? How?

Such questions are not created by words and cannot be abolished by words. But words do have the power to obscure them. And there is quite a real danger that this may happen.

It is so very tempting to allow one's attention from unwelcome facts to be diverted by discussion about definitions or the choice of the best terms or anything else that is not relevant. One may think that one is making an honest attempt to formulate a problem more clearly; but one is really, by one's exaggerated preoccupation with definitions, trying unconsciously to dodge it.

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