The Tacit Dimension

Some authors have pointed out that machines have a purposive character which cannot be derived from the laws of physics and chemistry. But, to obtain the actual relationship of the principles of a machine and the laws governing its parts, we must consider the nature of a machine as a comprehensive entity. This will serve also to consolidate and deepen our conception of the logical structure governing such entities, for in this case it is possible to define with a fair degree of precision the relation by which the parts are integrated to the entity formed by them. I have presented this analysis often elsewhere, and shall therefore state its main points here without arguing them.

Machines are defined by their operational principles, which tell us how the machine works. These operational principles include the definition of the parts composing the machine and give an account of their several functions in the working of the machine; they also state the purpose which the machine is to serve. The machine relies for its functions on certain physical-chemical processes involved in their joint operation. No more need be required in this respect than that the material of the machine be solid and be ruled by the laws of mechanics.

Engineering and physics are two different sciences. Engineering includes the operational principles of machines and some knowledge of physics bearing on these principles. Physics and chemistry, on the other hand, include no knowledge of the operational principles of machines. Hence a complete physical and chemical topography of an object would not tell us whether it is a machine, and if so, how it works, and for what purpose. Physical and chemical investigations of a machine are meaningless, unless undertaken with a bearing on the previously established operational principles of the machine. But there is an important feature of the machine which its operational principles do not reveal; they can never account for the failure and ultimate breakdown of the machine. And here physics and chemistry effectively come in. Only the physical-chemical structure of a machine can explain its failures. Liability to failure is, as it were, the price paid for embodying operational principles in a material, the laws of which ignore these principles. Such a material will eventually cast off the yoke of such foreign control.

But how can a machine which, as an inanimate body, obeys the laws of physics and chemistry fail to be determined by these laws? How can it follow both the laws of nature and its own operational principles as a machine? How does the shaping of inanimate matter in a machine make it capable of success or failure? The answer lies in the word: shaping. Natural laws may mould inanimate matter into such patterns as that of the solar system. Other shapes can be imposed on matter artificially, and yet without infringing the laws of nature. The operational principles of machines are embodied in matter by such artificial shaping. These principles may be said to govern the boundary conditions of an inanimate system - a set of conditions that is explicitly left undetermined by the laws of nature. Engineering provides a determination of such boundary conditions. And this is how an inanimate system can be subject to a dual control on two levels: the operations of the upper level are artificially embodied in the boundaries of the lower level which is relied on to obey the laws of inanimate nature, i.e. physics and chemistry.

We may call the control exercised by the organisational principle of a higher level on the particulars forming its lower level the principle of marginal control. The principle of marginality could be recognised already in the way I described some hierarchies of human performances. You can see, for example how, in the hierarchy constituting speechmaking, successive working principles control the boundary left indeterminate on the next lower level. Voice production, which is the lowest level of speech, leaves largely open the combination of sounds into words, which is controlled by a vocabulary. Next, a vocabulary leaves largely open the combination of words into sentences, which is controlled by grammar. And so it goes.

Moreover, each lower level imposes restrictions on the one above it, even as the laws of inanimate nature restrict the practicability of conceivable machines; and again, we may observe that a higher operation may fail when the next lower operation escapes from its control. Words are drowned in a flow of random sounds, sentences in a series of random words, and so on.

In a broad way we can see this principle of marginal control operating also in the hierarchy of biotic levels. The vegetative system, sustaining life at rest, leaves open the possibilities of bodily movement by means of muscular action, and the principles of muscular action leave open their integration to innate patterns of behaviour. Such patterns leave open, once more, their shaping by intelligence, the working of which offers, in its turn wide-ranging possibilities, for the exercise of still higher principles in those of us who possess them.

These illustrations of the principle of marginality should make it clear that it is present alike in artifacts, like machines, in human performances, like speech; and in living functions at all levels. It underlies the functions of all comprehensive entities having a fixed structure. We may confidently rely, therefore, on our analysis of machines to declare that the predominant view of biologists - that a mechanical explanation of living functions amount to their explanation in terms of physics and chemistry is false. Moreover, the conclusion that machines are defined by the fact that boundary conditions expressly left open by physics and chemistry are controlled by principles foreign to physics and chemistry, makes it clear that it is in respect of its characteristic boundary conditions that a mechanically functioning part of life is not explicable in terms of physics and chemistry.

This is not to deny that there is a great deal of truth in the mechanical explanation of life. The organs of the body work much like machines, and they are subject to a hierarchy of controls, exercised by an ascending series of mechanical principles. Biologists pursuing the aim of explaining living functions in terms of machines have achieved astounding Success. But this must not obscure the fact that these advances only add to the features of life which cannot be represented in terms of laws manifested in the realm of inanimate nature. 

(Polyanyi: The Tacit Dimension, Routledge Kegan Paul).