quantitative specifications unconnected with qualitative ones, or with processes free of opposition or dialectical contradiction. For example, we can very well describe a physical system in which the law of gravity did not hold in the form we know it. Thus bodies might attract each other with a force not inversely proportional to the square of their distance; or in the formulation made by general relativity theory, quite different geometries might apply. But what of a physical system in which forces acted between bodies but none of these forces were attractive? It is not very hard to see that such a system is an "absurdity". One can talk of such a system, but it is mere "fantasy". So in Dialectics of Nature Engels wrote about the necessary correlation of attraction and repulsion in physical systems, and showed that this was a case of the more general principle of "unity of opposites". Again, one can speak of a system in which quantitative changes did not involve qualitative ones. But how could we recognise or measure any quantitative changes unless there were recognisable qualities connected with them? And how could we formulate generalisations or "laws" governing such changes except in terms of such connection? As Engels put it in Dialectics of Nature, "the dialectical laws are really laws of development of nature, and are valid for theoretical natural science". They are "laws of development of nature", and theoretically "valid", because no material system and its laws could be described in concrete terms except in conformity with the dialectical principles. Hence they are always and necessarily found exemplified in natural as well as social science, whenever we undertake "the concrete analysis of concrete conditions". Their formulation is first suggested as a result of observing their occurrences and exemplification (somewhat as mathematics is first arrived at from observation and practical application, and not produced ready‑made a priori out of people's heads, the concepts of number and measure, just like those of quantity, quality, opposition, and so on, being derived from experience). But at the same time, once they are formulated, the necessity, of dialectical laws, and consequently their logical distinction from empirical laws, can be demonstrated, and their formulation be then systematically corrected and made more exact in the procedure of demonstration.
5. DIALECTICS AND MATERIALISM
An important consequence of this account of dialectics is that it renders invalid the separation so often made in expounding Marxist philosophy between materialism and dialectics.
In his little book on Dialectical Materialism (which was extracted from the larger History of the Communist Party of the Soviet Union, 1938) J. V. Stalin separated materialism from dialectics by saying that the former was "the theory" and the latter "the method". Mechanistic or pre‑dialectical materialism is, perhaps, "a theory"—that is to say, a "metaphysical theory" which attempts to state the ultimate constitution and structure of the universe. But dialectical materialism is not "a theory" in that sense, or in any sense of the word in which "theory" may be contrasted with "method". The fact is that the derivation and substantiation of the principles of dialectics is at the same time that of the principles of materialism—they are inseparable and are principles of exactly the same sort, being demonstrated in terms of the correct marshalling of categories in informative discourse.
Thus, for example, Ryle was quite right in calling the idealist theory of "the ghost in the machine" a "category mistake", even if one may disagree with his account of category. And so is it a category mistake to adopt the more general idealist approach that "thinking is prior to being", as it is to adopt such typically "undialectical" ideas as that things are what they are independent of their relations with other things and of their modes of coming into being and ceasing to be, or that qualitative and quantitative changes take place independently, or that processes proceed fre