John Maynard Keynes once described Isaac Newton as ‘the last of the magicians’. Keynes was playing a little when he made this remark; but the fact that he could make it at all is symptomatic of a major revolution in the history of science. In the bad old days, historians assumed a sharp dichotomy between the rational heroes of experimental science, and the morass of irrational superstition they were fighting against. Now we are much more sensitive to ways in which the earlier modern scientists were still children of their own era. So much so, that it has become a commonplace to stress the continuity between mechanistic science, and rival interpretations of the world based on mystical meanings, vital principles, world souls, and so on.

In the case of philosophy, on the other hand, historians have neglected similar continuities affecting the earlier modern philosophers. This is odd, because at least until the end of the seventeenth century, the scientist and the philosopher were generally one and the same person. For example, Newton’s almost exact contemporary, Gottfried Wilhelm von Leibniz, spent much of his time working on intrinsically mathematical, scientific, and technical problems: the infinitesimal calculus, binary arithmetic, the laws of mechanics and of planetary motion, and the design of calculators, clocks, lenses, and water pumps. Yet today, Leibniz is chiefly remembered as a pure philosopher, for his theories about logic, language, the structure of reality and how we know it, the nature of the human mind, and freedom and causality.

Leibniz is also an excellent example of a thinker who was immersed in practices and beliefs which most twentieth-century scientists would class as downright irrational. For much of his life he was involved in various alchemical schemes for making gold, and he enjoyed a considerable reputation as an adept. As for his beliefs about the nature of reality, he held that everything ultimately consisted in masses of tiny animals, every animal being a colony of smaller ones, and so on ad infinitum; that the whole scope and history of the universe was represented in the least part of it at any moment; that animals had souls, and that they pre-existed birth and survived death. These are only samples of Leibniz’s stranger theories.

When we are dealing with scientific achievements, it is easy enough to bracket off any beliefs which embarrass us today. Newton’s work made its mark without anyone’s needing to know that he too was an alchemist, or that he believed he was merely rediscovering what the Hebrew prophets already knew. Similarly, it so happens that Leibniz’s independent discovery of the infinitesimal calculus arose out of his attempts to square the circle; but this fact is of no more than historical interest. In philosophy, however, there is no obvious way of disentangling offending beliefs and concepts. There is no given line of demarcation between genuine philosophy in the modern sense, and mystical speculation.

If we feel a problem about the contamination of Leibniz’s philosophy by irrational factors, then it is a problem of our own making. We have certain preconceptions about what beliefs are within the range of acceptability for a twentieth-century scientist or philosopher, and what is to count as loony or cranky. But if we approach the history of philosophy armed with such preconceptions, we shall find it difficult to understand an age in which there was no comparable dichotomy between rational and irrational belief.

There is, however, a more fundamental drawback. What is important about a philosophical system is not what happens to be true or false, but the conceptual categories it is appropriate to adopt for describing reality. It is precisely because reality has been conceptualised in radically different ways at different periods that the history of philosophy retains its value as a subject of more than antiquarian interest. In effect, the history functions as a sort of conceptual gene bank: a repository of alternative perspectives. If we insist on interpreting earlier philosophers from a twentieth-century approach, we are discounting the possibility of learning from them by rediscovering now unfashionable perspectives. You might expect an interest in history to be a sign of conservatism: in fact it is ambivalent. Some historians are indeed earning their living by rewriting history in anodyne terms acceptable to our own generation. Others cherish history more for its revolutionary implications.

So, what perspective is appropriate for understanding the unfamiliar blend of the rational and the irrational which we find in Leibniz’s philosophy? Conveniently, this is a question which can be answered from within Leibniz’s philosophy itself. The answer is what you might call a ‘perspectivist perspective’ on the history of philosophy. To explain what I mean, I can do no better than quote Leibniz’s own words [from a 1698 article defending himself against the famous sceptic, Pierre Bayle, in Philosophischen Schriften, ed. Gerhardt, vol. IV, pp.523-4]. He writes:

Or, as he put it more aphoristically [in a letter of January 1714 to the French courtier, Nicolas Remond, Gerhard, vol. III, p.607]:

In practice, Leibniz’s perspectivism committed him to a view of philosophical progress as a kind of dialectical synthesis. It would be anachronistic to read him as anticipating the sophisticated theories of dialectics evolved by Hegel, Marx, and others. Leibniz believed that objective truth was simply a summation of what was positive in the subjective beliefs of different individuals. To give an analogy, a number of people looking at a cube from different angles will all perceive it differently. There is, however, an ideal mathematical description of the cube which transcends the limitations of each individual perspective, and from which the individual perspectives themselves can be calculated. If two perceivers claim that the cube is really only just as it looks to them, they are mistaken not in what they assert, but only in their refusal to recognize the equal validity of alternative points of view. They are indeed narrowing their horizons by taking their own limited viewpoints as constituting the whole truth.

Applied to philosophical disputes, the notion of perspective is, of course, only a metaphor. As far as concerns the denial of alternative viewpoints, there is no problem. Just as observers might deny the existence of the far side of a cube, so there might be a dichotomy between, say, materialist and spiritualist philosophers, each denying what the other validly perceives. More problematic is how there could be anything corresponding to the objective description of the cube itself. What could make materialism and spiritualism fall into place as different and incomplete, yet mutually compatible, perspectives on a single truth? Surely the great issues polarise philosophies as direct contradictories of each other: either reality is wholly material, or it also includes a spiritual element; either there are purposes in nature, or it is purely mechanical; either everything that happens is causally determined, or some beings have free will; either the universe is created and governed by Divine Providence, or it is the outcome of chance.

To achieve a synthesis, we need what one might call a ‘transconceptualisation’ of the concepts. No dialectical synthesis is conceivable as long as philosophical problems are conceptualised in ways which present us with such dichotomies. Leibniz’s method consisted in finding new ways of conceptualising reality which enabled each pole of a dichotomy to be seen as a partial and distorted view of the truth. He applied his method to a wide range of philosophical, scientific, religious, and political questions. Here I have time to consider only the one example I began this talk with, namely the dichotomy between modes of thought which are nowadays accepted as rational, and those which I loosely refer to as ‘occultist’.

During the middle of the seventeenth century, there was a growing consciousness of a divide between two rival and apparently incompatible world-views. On the one hand, there was the materialist, mechanist picture, according to which the world was to be understood exclusively in terms of particles of matter interacting with each other in accordance with the laws of motion. On the other hand, there was the spiritualist, occultist picture, according to which some or all natural phenomena were to be understood in terms of the sympathies and antipathies of spiritual beings acting purposefully. An important dimension of Leibniz’s philosophy was his project of synthesising these two approaches through a new set of concepts which would do justice to the insights of each.

Leibniz’s best known concept is that of a monad, literally a ‘unit’. At all periods, commentators have found it difficult to decide whether his monads were fundamentally infinitesimal atoms of matter, though described somewhat paradoxically, or whether they were thoroughly spiritual realities, little different from the vital principles of occultist philosophers. Along with Leibniz himself, it could be said that both interpretations are right in what they assert, and wrong in what they implicitly deny. His monads were indeed both the atomic foundations of the material world, and the basis of an organic and holistic interpretation of reality. But for his synthesis to work, his ultimate entities had to be neither simply material, nor spiritual — they had to be immaterial, but without ending up as the invisible spirits, demons, and angels, and the such-like of the occultist world-view.

In fact he accepted the basic assumption of the new philosophy that explanations of particular events had to be in terms of mechanical interactions between material particles. He was, indeed, an extremist, in asserting that all events, including human thoughts and behaviour, could be given purely mechanical explanations. For Leibniz, materialists were definitely right in what they asserted, and spiritualists were wrong to deny the universality of mechanical causation. On the other hand, he also saw the orthodox mechanical philosophy as hopelessly one-sided. In his view, its limitations could be made good only by recognising the positive insights of spiritualism. I shall outline just two of the more serious shortcomings he found in crude materialism.

The first difficulty was that the atomic constituents of matter, or spatially extended substance, could not themselves be spatially extended. This is a consequence of the infinite divisibility of space. However small you take atoms to be, you can still consider them as compounds of smaller parts, and hence not truly atomic. But if you make atoms into indivisible, mathematical points, then they are too small to be characterised by the spatial properties traditionally held essential to matter, such as solidity, size, and shape.

Instead, Leibniz defined the essence of matter in terms of its dynamic properties. What distinguished solid matter from empty space, or from immaterial things like ghosts or rainbows, was essentially its power to resist penetration or acceleration. He thus circumvented the problem of indivisibility by making the essence of matter a power, or force, or energy — the terms were interchangeable in his day. Since there was no logical absurdity in conceiving a quantum of energy as existing at a mathematical point, Leibniz’s monads could therefore function as energy-points.

The second main difficulty he saw in materialism was its inability to explain the basic process of mechanical interaction itself, namely the transfer of energy from one material particle to another by pushing or colliding into it. At any level, it was possible to give a provisional explanation in terms of the elasticity of the particles composing colliding bodies. So, when two objects collide, the particles of each are first compressed, and then spring back again from each other, thus reconverting elastic forces back into kinetic energy. But this gets us no nearer to understanding the underlying process of energy transference, since it presupposes precisely the same processes at a more microscopic level: the elasticity of the particles can be explained only in terms of their elastic sub-particles, and so on to infinity. To explain mechanical interaction as mediated by a sub-mechanism merely postpones any solution to the problem of interaction itself.

As before, Leibniz got round the difficulty by conceptualising the situation in a radically different way. He saw it as a mistake to picture mechanical interaction as consisting in the handing over of parcels of energy from one physical object to another. Really, the colliding body merely functioned as a stimulus to which the other body responded of its own accord. As we all know, every force has an equal and opposite reaction. Leibniz held that colliding bodies reacted by virtue of their own reactive forces. In his terminology, all action was spontaneous.

However, this gave rise to a new difficulty. Orthodox mechanists explained everything as blind reactions to imposed forces. But if all actions were to be spontaneous, how could monads register what stimuli they were receiving, and react to them in such a way as to avoid complete chaos in the universe? In order to preserve the harmony of things, monads had, in some sense, to ‘know’ what everything else was doing, and to be motivated to promote the harmony of the whole.

In the light of these requirements, it is hardly surprising that Leibniz was reduced to metaphor and analogy. In order to express his ideas, he adopted the terminology of spiritualism. He said that monads were like souls, only unconscious: they were sources of energy and spontaneous activity; they perceived their spatial environment without themselves being spatial; and they acted purposefully in accordance with a motivation towards the best

Leibniz’s dialectical immaterialism transcends any crude dichotomy between the materialism of the mechanistic philosophy, and the spiritualism of the occultists. From a materialist perspective, his philosophy would appear hopelessly contaminated by vital principles, and all that they imply. Yet from a spiritualist perspective, he would appear horrifyingly generous to materialism, in conceding that the only admissible explanations of natural phenomena were purely mechanical.

As it turns out, his theories were prophetic of twentieth-century developments. The idea that matter and energy are interconvertible, that particles are concentrated fields of force, and that organisms are more than just the sums of their parts are thoroughly consistent with Leibniz’s philosophy. The ultimate constituents of reality must differ in kind from the material objects they explain, and this inevitably makes them more like spiritual substances. Despite his crudely spiritualist imagery, Leibniz was really no more ready than any modern physicist to leap to the other, occultist extreme, and view nature as a battleground of opposed and allied spirits and demons. An immaterialist synthesis is equally hostile to both extremes.

Physicists do not often look for inspiration in the philosophies of the past. Today it is only of historical interest that Leibniz’s view of nature was in many respects closer to modern physics than that of his materialist contemporaries. But in philosophy, there is plenty of scope for his example still to be followed. To follow his example is to accept that two or more distinct philosophical perspectives can be right in what they assert. If we find it a problem to provide a conceptual framework which can accommodate both without contradiction, then this probably means that we are trapped within fashionable dichotomies. One of the best ways of escaping from fashion is to look back to the wisest of our predecessors, whose traps were at least different from our own.

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