One thing that surprises me about professional philosophers is the readiness with which we are prepared to dismiss each other as cranks, madmen, enemies of reason, loonies, and so on. We can imagine cases in which almost anyone would agree that such judgments were justified; yet there are others when such abuse looks more like a merely dogmatic refusal even to hear the other man’s arguments - and that is a kind of behaviour which is itself open to the charge of irrationality. I do not see how it is possible to maintain any faith in philosophy as a rational activity unless we have some idea of how to draw the line between the sane and the mad, the reasonable and the absurd, the rational and the superstitious. Yet even the possibility of drawing that line at all is called into question by the lessons of history and of anthropology. What grounds have we for supposing that today’s orthodoxies will not seem weird and superstitious to future generations? Indeed, I am sure that all of us have some favourite candidates for such a fate. But if we move too far in the direction of relativism we will arrive at the unacceptable conservative position that the sole arbiter of rationality at any given time is the current established orthodoxy, so that superstition becomes equivalent to intellectual deviance from the norm. Or we could go still further, and end up with a sort of conceptual anarchism, according to which no-one’s beliefs would be saner than anybody else’s.

This tension between the two opposing epistemological tendencies, towards absolutism on the one hand and towards relativism on the other, has serious historiographical repercussions. Thus the relativist is highly motivated to prove his point by finding as many differences as possible between past and present ideas. An example that springs to mind is the way in which Frances Yates is always making as much as she can of occult influences on sixteenth- and seventeenth-century thinkers. [1] Absolutists, on the other hand. have tended to interpret the past in terms of a crude polarisation between rational goodies and superstitious baddies. This has caused problems particularly in the history of seventeenth century science. What are we to do about the crankier beliefs and activities of the heroes of the dawning age of enlightenment? The commonest solution has been to ignore them: for example, there must until recently have been what amounts to deliberate suppression of the facts about Newton’s alchemical activities and his rather weird religious beliefs. Another approach is to whitewash the prima facie irrational elements. Thus Richard van Dülmen writes as follows about the alchemical society Leibniz belonged to (I shall say something about this society shortly):

But, as I have argued elsewhere, [3] weak evidence for the existence of a society with extreme characteristics does not collapse into strong evidence for the existence of a society with more moderate characteristics. Yet another approach is to commend the theses you approve of as the product of sound reasoning, and explain the rest away as the product of mere causes. Thus Hidé Ishiguro writes:

At this point I cannot resist quoting a passage from David Brewster’s Memoirs of the Life, Writings and Discoveries of Sir Isaac Newton, which comes as near as is possible to exemplifying all three approaches at once:

In short, I believe that there is a double problem here: first, that of finding a satisfactory way of distinguishing the rational thinker from the crank which does justice both to the fallibility of the former and to the merits of the latter; and secondly that of giving a balanced account of the strengths and weaknesses of historical figures. In this paper I want to concentrate on one particular case, namely that of Leibniz’s involvement in alchemy, and see what conclusions can be drawn from it which may shed light on the more general problems. I shall start by outlining the story of Leibniz’s involvement as neutrally as I can.

In September 1666, when he was 20, Leibniz left the University of Leipzig, because he was refused a doctorate on the grounds that he was too young (apparently this was at the instigation of the wife of the Dean of the Arts Faculty, who was ‘maliciously disposed towards him’ [6]). He then went to the University of Altdorf, near Nuremberg, where on the 15th of November he presented his thesis Disputatio de casibus perplexis in jure, and on the 22nd of February 1667 he was formally awarded the degree of Juris Utriusque Doctor. It seems that for a few months, probably from December 1666 to March 1667, he was given some sort of secretarial employment by a group of Nureremberg intellectuals interested in alchemy, but there is almost no firm, evidence as to what he did for them. The story that they were Rosicrucians is almost certainly a mistake.

After spending some time in Frankfurt, Leibniz was eventually given the post of Consiliarius Revisionum by the Elector of Mainz. [7] It is not clear what his official duties were, but unofficially it is quite probable that they had something to do with his reputation as an alchemist. Such dissimulation would not be without precedent. Leibniz himself writes of the alchemist Johann Kunckel that he was the Chamberlain of the Elector of Saxony,

Since the evidence for Leibniz’s reputation as an alchemist is rather skimpy, I shall briefly run through what there is, under three heads:

Firstly, there survive a number of letters written to him on the assumption that he was well informed about alchermy. For example, the Jesuit alchemist Kochansky wrote to him in 1671:

Secondly, Leibniz himself boasted of his wide acquaintance of and correspondence with alchermists. As he wrote to Carcavy in 1671:

Thirdly, he claims that various German princes pestered him for his services. As he wrote to Kochansky in 1696:

And in the same year he wrote to Gotttried Thomasius, the son of his philosophy supervisor at Leipzig:

It seems that at least one of these princes succeeded in getting something out of him, for in 1698 he wrote to Peter Müller:

He doesn’t say who he wrote this ‘harmony of the philosophers’ for; but since he places it in the year 1667–8, his patron must surely have been the Elector of Mainz, to whom he wrote as follows in 1668:

After this, in 1676, he transferred to the Duke of Hanover as librarian. Whether his alchemical reputation had anything to do with this appointment too, there is no way of telling — though it is perhaps not irrelevant that he was used as a sort of free-lance minister of technology, and was given large sums of money to develop a calculating machine which would reduce the labour costs of the Hanoverian administration by making large numbers of clerical workers redundant; and also a wind-powered drainage system for improving the productivity of the mines in the Harz Mountains. He was also deputed to negotiate with chemists (or alchemists — the distinction had not yet jelled) such as Brand, the discoverer of phosphorus. Brand, incidentally, was working on a clue in some alchemical text, that the philosophers’ stome was to be found in the dregs of the human body. He took this literally, tried distilling urine and found phosphorus. Quite apart from the possibility of its being a stage on the route to the stone, it had considerable monetary value as a curiosity for the then fashionable scientific demonstrations. But to produce it commercially needed an awful lot of urine. Hence the contract to produce it in the Harz Mountains, where there were an awful lot of miners producing urine.

But whatever the implicit terms of his contract with the Duke of Hanover, Leibniz certainly maintained an interest in alchemy. Thus in about 1676, he entered into an agreement with Georg Hermann Schuller and Johann Daniel Crafft that they should share the profits from any success in making gold. Apparently some itinerant alchemist was also involved, since in his correspondence with Leibniz, Schuller repeatedly reports on the whereabouts of ‘Our Proteus’ and ‘Our Goldmaker;’ and it is also possible that Johann Joachim Becher was party to the agreement, since Schuller talks of him and Crafft working together on the transmutation of metals. Leibniz’s role is not made clear, but it seems to have been confined to that of supplying money and theoretical advice. It is indicative of the current attitude to alchemy that Leibniz went to great lengths to conceal the true reason for his sending money to Schuller in Holland, by pretending that it was for the purchase of books, and by suggesting a secret code for use in their correspondence.

A few years earlier Leibniz may have had a similar arrangement with Paul Barth and Peter Paul Metzger. In December 1670, Barth answers Leibniz’s request for information about the progress of ‘our philosophical work’ by giving a detailed account of his difficulties, which included Metzger’s promotion to public office, and asking Leibniz’s advice on how to proceed. Much later, in 1688, Metzger sends his greetings to Leibniz and Barth, and reminisces about their alchemical discussions. He writes:

His comment that Leibniz once believed that the philosophers’ stone could be developed from vitriol is important, since it adds a new dimension to Leibniz’s own more neutral statement in the Miscellanea Berolinensia of 1710: he reports how in his youth he had solved two alchemical riddles, and then continues:

Perhaps Leibniz is concealing the fact that he is referring to his very own ‘harmony of the philosophers,’ which would have consisted in reconciling Basil Valentine’s vitriol with Stephen of Alexandria’s arsenic.

But to return to hard facts, apart from co-operative endeavours between friends, Leibniz was for a long time willing to invest considerable sums of money in the projects of individual alchemists, the latest example I can find being that of Math. Starck in 1693. And even where there is no evidence of his demonstrating his confidence in such a tangible way, there are records of many occasions on which he showed a keen interest in learning about and testing claims that the philosophers’ stone had been found, and in some of these he seems to have thought that the prospects were encouraging. In particular he considered it worthwhile suggesting to Duke Johann Friedrich in 1678 that Wenzel Seyler should be tested, and in 1679 that the Duke should be ready to imitate Becher’s process for getting gold from sand (though he might already have considered this to be a case of extraction rather than of transmutation). Two years later he was encouraging Duke Ernst August to test Captain Vierort, and as late as 1698 we find him writing to Peter Müller:

I really wish I could look at a specimen of the true Tincture which you are expecting from an adept.

Indeed, it is reported that while on his deathbed Leibniz spent part of his last hours discussing with his physician, Dr. Seip, the case of the famous alchemist Furtenb ach, who had claimed to have changed half an iron nail into gold.

It therefore appears indisputable that for much of his life Leibniz considered goldmaking to be a worthwhile endeavour, although we do not know how far he pursued this aim by actual experiments in the laboratory. He would certainly have had adequate facilities, if not the time, in Nuremberg and in the Harz Mountains; but the only occasion on which he even hints that he might himself have had any laboratory experience is when he writes to Peter Müller:

So far we have a consistent picture of a life-long and genuine, even if somewhat restrained, involvement in alchemy. But there is one jarring piece of evidence from the biography of Leibniz written by his secretary Eckhart just after his death. It has to be taken very seriously, since it is the sole source for our knowledge of the episode of the alchemical society of Nuremberg, and it does read like an honest report of what Leibniz presumably told Eckhart towards the end of his life. The reason why it jars is because it portrays him as having only the one contact with the world of alchemy, and as laughing it off as only a youthful prank. The passage runs as follows:

This passage has a double significance. Firstly, it presupposes a new-found consciousness of a distinction between respectable science and the crankiness of alchemy. Secondly, Leibniz was clearly embarrassed by his earlier dalliance with alchemy, and wanted to give the impression that even at the time he saw it as intellectually disreputable. But if Eckhart has reported him correctly, Leibniz must surely have been dishonest to the point of mendacity, given the independent evidence for his continuing involvement. Moreover, although Leibniz hated throwing away anything he had written, and nearly always carefully preserved early drafts and clean copies of his letters and articles, despite this, almost no letters survive from the period when he was most involved in alchemy. This suggests that, given the frame of mind portrayed by Eckhart, Leibniz may have deliberately tried to destroy all the evidence of his involvement, and have missed only the occasional reference amidst the vast mass of his papers. But this still leaves unanswered the question: why was Leibniz so embarrassed? If he had accepted all sorts of superstitious beliefs, performed magic rites, composed writings consisting largely of mumbo-jumbo, and so on, his embarrassment would have been understandable. But in fact this is not the case. As far as we know, his interest was always sober and rational, and his increasing scepticism was fired not by any emotional revulsion against the occult, but by a reasoned calculation that the methods of traditional alchemy were unlikely to succeed of their purpose. So I must first explain in greater detail what Leibniz’s approach to alchemy was like in his youth, and in his maturer period of scepticism. [9]

Leibniz always believed in the theoretical possibility of creating gold, apparently on the general metaphysical grounds that matter is one. More specifically the possibility of transmutation was also implicit in the doctrines of his Hypothesis Physica Nova of 1671, which excluded truly elementary chemical substances (the nearest being smaller or larger and exhausted or distended bubbles, corresponding to volatile or fixed alcali or acid respectively). On a number of occasions he makes it explicit that one of the merits of his hypothesis is that it can account for the tincture and the alcahest, if such things exist. Nor is it surprising that he should have believed in the practical as opposed to the merely theoretical possibility of transmutation, since he held that all metals had already been generated from more elementary substances through natural processes during the course of the earth’s evolution; and what nature can do, art can imitate. In addition, he was aware of many examples (real or imaginary) of the use of laboratory processes to bring about radical changes in physical substances, or to extract substances with amazing properties from the most unpromising materials. One instance of this was the production of phosphorus from urine, which we have already alluded to; and Leibniz may perhaps for a time have shared its discoverer’s hope that it would yield the philosophers’ stone. Besides, a number of cases of alleged transmutation, such as those performed by Baron de Chaos and by Wenzel Seyler, had been authenticated by the most irreproachable of witnesses.

But although he was enthusiastic, he was certainly never credulous. He was always careful to test claims that transmutation had been or could be successfully carried out, and there is no record of his ever having been convinced by any particular recipe. For instance, he pestered Crafft and Schuller for detailed information about their processes, and when he finally got a long explanation from Schuller, he noted on the letter:

Again, Landgrave Ernst once asked him why Becher, in his Närrische Weisheit und weise Narrheit, had ridiculed Leibniz for claiming to have invented a chariot that could travel from Amsterdam to Hannover in 6 hours; and Leibniz explained that it was because Becher was furious with him for having prevented ‘a certain alchemical folly he had in mind.’ From his earliest years he was aware of the mixture of fraud and stupidity that characterised the majority of self-styled ‘sons of the art,’ as he once called them, and he singled out alchemical writings as examples of reprehensible obscurity. On the other hand, he recognised that uneducated and misguided alchemists were responsible for as many useful discoveries as the intellectual establishment, and drew the conclusion that the enthusiasm and abilities of all should be harnessed to a properly organised programme of scientific research. And he remarked that even if the stone did turn out to be an illusion, the hope of finding it would still have stimulated much worth-while investigation.

However, by the 1690s he had gradually changed his mind about both the possibility and the desirability of transmutation, and had become openly critical of people like Tollius, Crafft and Becher for dissipating their energies on vain alchemical dreams. The reason he most commonly gives for doubting that anyone would succeed in making gold is the empirical one that all previous attempts have failed, though he is often careful to add that this does not show that transmutation is absolutely impossible. Thus, he writes to Hartsoeker in about 1710:

But, as he writes to Kochansky in 1696, the chance of success is so small that it is as irrational to devote oneself to searching for the stone as it is to give up everything on the assumption that one is going to win a lottery. More generally, and with a certain modern ring, he implies in a letter to Queen Sophie Charlotte that the claims of alchemists are discredited by their unfalsifiability as much as by lack of direct confirmation. But in addition to arguing at this empirical level, Leibniz also produced some theoretical grounds for doubting the possibility of making gold, though he was still prepared to recognise that he might eventually be proved wrong.

First, he seems to have come round to the view that, at least for all practical purposes, certain types of substance were specifically distinct, so that any prima facie case of transmutation would have to be considered as really only a mixture, in which the particles of the original substance lay concealed. But he did not lay much stress on this as an argument against transmutation, presumably because to do so would involve a petitio principii. Much more important is his discussion in his Oedipus Chymicus, published in 1710, in which he argued that it is difficult to imagine how anything could have the properties required of the philosophers’ stone, in particular the capacity to bring about a rapid increase in the density of a quantity of material much larger than itself. The alchemists’ conception of the stone as like a seed was doubly wrong, since it must be part of inorganic, not organic nature; and in any case the action of a seed would be far too slow. But, on the other hand, who would have conceived of the possibility of gunpowder without having experienced it first? He admitted that it was easier to imagine a quintessence of gold, which could be used to produce a strictly limited quantity of ordinary gold in the way that a mixture of alcohol and water would yield something analogous to wine; but this would not constitute true transmutation, and it could not increase the total amount of gold in the universe.

By the time he had come to the conclusion that the stone was unattainable anyway, he began to express concern about the damage its discovery would do to commercial life. Without a high-value medium of exchange we would return to the days when a peasant selling his produce in the town needed a cart to take his money back home. Thus the only lasting value of the philosophers’ stone would be scientific, in so far as its discovery would yield new knowledge of nature; but in that case scientists would be much more usefully employed on more promising channels of research.

In the light of all this evidence, it might seen that we could now breathe a sigh of relief, and single out Leibniz as a lonely beacon of rationality as we know it, amidst the fogs of seventeenth-century superstition which managed to engulf even the great Newton. But matters are not so simple. Consider, for exammple, the following sections from Leibniz’s Monadology. [10]

If I were asked to produce a text from Leibniz which would make obvious how straight and rational his philosophy was by the standards of modern scientific orthodoxy, the above passage would hardly be my first choice. Moreover, it is an unusually clear instance of one respect in which Leibniz’s contact with alchemical ideas had a permanent influence on the development of his metaphysics. A primitive form of his mature theory of monads is to be found in a document entitled De resurrectione corporum, and in an accompanying letter which he wrote for Herzog Johann Friedrich in 1671.[11] In this, he attempted to solve the problem of how God is to resurrect two distinct bodies if they have some pieces of matter in common (for example, if someone’s dead body re-enters the food chain through being eaten by worms). His solution depends on postulating an element in each substance which is additional to the three components generally recognised by alchemists, or ‘chemists’ as he calls them. Over and above the terra damnata, the phlegma and the caput mortuum, there must also be a subtler, more spiritual ‘kernel’. As he says in the De resurrectione corporum:

This spiritual kernel is the seat of the soul and the principle of organisation of the body; it is analogous to a mathematical point; it is qualitatively different in each individual substance; it can be neither created nor destroyed, but only expands or diminishes in its sphere of influence. In short, it is a semi-materialist and partial version of the monad of his mature philosophy. Because of its importance as containing the germ of his future metaphysics, I shall now quote most of’ the relevant part of his letter to Johann Friedrich. He writes:

He then uses the same concept to explain the phenomenon of phantom limbs: when the limb is cut off, the kernel retreats into the main body, and retains a trace of the limb which can still be felt. He continues:

The point of my quoting these lengthy passages is that it is all the more mysterious that Leibniz should have lied about his youthful interest in alchemy, if his specifically alchemical involvements were in fact innocent of any superstitious element, while the philosophical system by which he set so much store was deeply rooted in ideas which were utterly out of tune with the way in which science and philosophy were to develop during the eighteenth century.

I believe that a solution can be found on the following lines. Leibniz was always adamantly opposed to any form of occultism or superstition. In this he was perhaps harder to please than many philosophers today. Thus he attacked Descartes for thinking he could solve the mind/body problem by postulating forces which could influence physical events without violating conservation laws; he attacked Newton for basing his system on the occult force of gravitation, the meaningless supposition of an absolute spatio-temporal frame of reference, and divine intervention to stop the universe from running down; he attacked the obscurantism of logicians who believed in implication relations other than that of the identity of two tokens of the same type; and he attacked philosophers of science who thought that causation consisted in the transfer of something from the cause to the effect.

I do not think it is entirely a coincidence that these cases do seem to have a common factor. This is the using of words as if they denoted some real but hidden entity, when the known facts fail to justify any such supposition. Looked at from this point of view, I think it is right to say that Leibniz was consistently rational, since he was always at pains to furnish reasons for his spiritualist analysis of the nature of reality. His embarrassment about his association with alchemy is sufficiently explained as a feeling of guilt by association. As he himself had pointed out, alchemists were peculiarly prone to the vice of assuming that their private jargon had real meaning, and he was naturally eager to disassociate himself from that. Moreover, it would have looked very odd to his contemporaries if he publicly criticised others for believing in occult factors, while himself retaining a sympathy for an activity which was rapidly emerging as the paradigm of occult superstition as contrasted with rational science.

What now seems weird about Leibniz is certain aspects of his metaphysical system considered as a set of beliefs: he arrived at conclusions which are radically out of tune with the twentieth-century scientific world-view. But if we concentrate on the spirit with which he approached them, it is difficult to imagine anyone more rational. That is, he was never willing to assent to anything without a reason, nor to dismiss anything as superstitious or nonsense without being prepared to give a reason for dismissing it. To sum up: I would say that this view of rationality can be generalised, since it allows us to commend a thinker for his rationality (or blame him for the lack of it) without committing ourselves to the timeless validity of his conclusions.

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