1. Reason why Leibniz never wrote a magnum opusThe philosophy of Leibniz, though never presented to the world as a systematic whole, was nevertheless, as a careful examination shows, an unusually complete and coherent system. As the method of studying his views must be largely dependent upon his method of presenting them, it seems essential to say something, however brief, as to his character and circumstances, and as to the ways of estimating how far any given work represents his true opinions.
The reasons why Leibniz did not embody his system in one great work are not to be found in the nature of that system. On the contrary, it would have lent itself far better than Spinoza's philosophy to geometrical deduction from definitions and axioms. It is in the character and circumstances of the man, not of his theories, that the explanation of his way of writing is to be found. For evervthing that he wrote he seems to have required some immediate stimulus, some near and pressing incentive. To please a prince, to refute a rival philosopher, or to escape the censures of a theologian, he would take any pains. It is to such motives that we owe the Theodicee, the Principles of Nature and of Grace1, the New Essays, and the Letters to Arnauld. But for the sole purposes of exposition he seems to have cared little. Few of his works are free from reference to some particular person, and almost all are more concerned to persuade readers than to provide the most valid arguments. This desire for persuasiveness must always be borne in mind in reading Leibniz's works, as it led him to give prominence to popular and pictorial arauments at the expense of the more solid reasons which be buried in obscurer writings. And for this reason we often find the best statement of his view on some point in short papers discovered among his manuscripts, and published for the first time by modern students, such as Erdmann or Gerhardt. In these papers we find, as a rule, far less rhetoric and far more logic than in his public manifestoes, which give a very inadequate conception of his philosophic depth and acumen.
Another cause which contributed to the dissipation of his immense energies was the necessity for giving satisfaction to his princely employers. At an early age, he refused a professorship at the University of Altdorf2, and deliberately preferred a courtly to an academic career. Although this choice, by leading to his travels in France and England, and making him acquainted with the great men and the great ideas of his age, had certainly a most useful result, it yet led, in the end, to an undue deference for princes and a lamentable waste of time in the endeavour to please them. He seems to have held himself amply compensated for laborious researches into the genealogy of the illustrious House of Hanover by the opportunities which such researches afforded for the society of the great. But the labours and the compensations alike absorbed time, and robbed him of the leisure which might have been devoted to the composition of a magnum opus. Thus ambition, versatility, and the desire to influence particular men and women, all combined to prevent Leibniz from doing himself justice in a connected exposition of his system.
2. Functions of the commentator on LeibnizBy this neglect, the functions of the commentator are rendered at once more arduous and more important than in the case of most philosophers. What is first of all required in a commentator is to attempt a reconstruction of the system which Leibniz should have written -- to discover what is the berginning, and what the end, of his chains of reasoning, to cxhibit the interconnections of his various opinions, and to fill in from his other writings the bare outlincs of such works as the Monadology or the Discours de Metaphysique. This unavoidable but somewhat ambitious attempt forms one part -- perhaps the chief part -- of my purpose in the present work. To fulfil it satisfactorily would be scarcely possible, and its necessity is my only excuse for the attempt. As I wish to exhibit a coherent whole, I have confined myself, as far as possible, to Leibniz's mature views -- to the views, that is, which he held, with but slight modifications, from January 1686 till his death in 1716. His earlier views, and the influence of other philosophers, have been considered only in so far as they seemed essential to the comprehension of his final system.
But, in addition to the purely historical purpose, the present work is designed also, if possihle, to throw light on the truth or falsity of Leibniz's opinions. Having set forth the opinions which were actually held, we can hardly avoid considering how far they are mutually consistent, and hence --since philosophic error chiefly appears in the shape of inconsistency -- how far the views held were true. Indeed, where there is inconsistency, a mere exposition must point it out, since, in general, passages may be found in the author supporting each of two opposing views. Thus unless the inconsistency is pointed out, any view of the philosopher's meaning may be refuted out of his own mouth. Exposition and criticism, therefore, are almost inseparable, and each, I believe, suffers from the attempt at separation.
3. Two types of inconsistency in his philosophyThe philosophy of Leibniz, I shall contend, contains inconsistencies of two kinds. One of these kinds is easily removed, while the other is essential to any philosophy resembling that of the Monadology. The first kind arises solely through the fear of admitting consequences shocking to the prevailing opinions of Leibniz's time -- such are the maintenance of sin and of the ontological argument for God's existence. Where such inconsistencies are found, we, who do not depend upon the smiles of princes, may simply draw the consequences which Leibniz shunned. And when we have done this, we shall find that Leibniz's philosophy follows almost entirely from a small number of premisses. The proof that his system does follow, correctly and necessarily, from these premisses, is the evidence of Leibniz's philosophical excellence, and the permanent contribution which he made to philosophy. But it is in the course of this deduction that we become aware of the second and greater class of inconsistencies. The premisses themselves, though at first sight compatible, will be found, in the course of argument, to lead to contradictory results. We are therefore forced to hold that one or more of the premises are false. I shall attempt to prove this from Leibniz's own words, and to give grounds for deciding, in part at least, which of his premisses are erroneous. In this way we may hope, by examining a system so careful and so thorough as his, to establish independent philosophical conclusions which, but for his skill in drawing deductions, might have been very difficult to discover.
4. His premissesThe principal premisses of Leibniz's philosophy appear to me to be five. Of these some were by him definitely laid down, while others were so fundamental that he was scarcely conscious of them. I shall now enumerate these premisses, and shall endeavour to show, in subsequent chapters, how the rest of Leibniz follows from them. The premisses in question are as follows:
5. Course of the present workThe course of the present work will be as follows: Chaptcrs II.-V. will discuss the consequences of the first four of the above premisses, and will show that they lead to the whole, or nearly the whole, of the necessary propositions of the system. Chapters VI.-XI. will be concerned with the proof and description of Leibniz's Monadism, in so far as it is independent of final causes and the idea of the good. The remaining chapters will take account of these, and will discuss Soul and Body, the doctrine of God, and Ethics. In these last chapters we shall find that Leibniz no longer shows great originality, but tends, with slight alterations of phraseology, to adopt (without acknowledgment) the views of the decried Spinoza. We shall find also many more minor inconsistencies than in the earlier part of the system, these being due chiefly to the desire to avoid the impieties of the Jewish Atheist, and the still greater impieties to which Leibniz's own logic should have led him. Hence, although the subjects dealt with in the last five chapters occupy a large part of Leibniz's writings, they are less interesting, and will be treated more briefly, than the earlier and more original portions of his reasoning. For this there is the additional reason that the subjects are less fundamental and less difficult than the subjects of the earlier chapters.
6. Influences which formed Leibniz's opinionsThe influences which helped to form Leibniz's philosophy are not directly relevant to the purpose of the present work, and have, besides, been far better treated by commentators3 than the actual exposition of his final system. Nevertheless, a few words on this subject may not be amiss. Four successive schools of philosophy seem to have contributed to his education; in all he found something good, and from each, without being at any time a mere disciple, he derived a part of his views. To this extent, he was an eclectic; but he differed from the usual type of eclectic by his power of transmuting what he borrowed, and of forming, in the end, a singularly harmonious whole. The four successive influences were: Scholasticism, Materialism, Cartesianism, and Spinozism. To these we ought to add a careful study, at a critical period, of some of Plato's Dialogues.
Leibniz was educated in the scholastic tradition, then still unbroken at most of the German universities. He obtained a competeut knowledge of the schoolmen, and of the scholastic Aristotle4, while still a boy; and in his graduation thesis, De Principio Individui, written in 1663, he still employs the diction and methods of scholasticism. But he had already, two years before this time (if his later reminiscences are to be trusted), emancipated himself from what he calls the "trivial schools5," and thrown himself into the mathematical materialism of the day. Gassendi and Hobbes began to attract him, and continued (it would seem) greatly to influence his speculations until his all-important journey to Paris. In Paris (with two brief visits to England) he lived from 1672 to 1676, and here he became acquainted, more iutimately than he could in Germany, with Cartesianism both in mathematics and philosophy -- with Malebranche, with Arnauld the Jansenist theologian, with Huygens, with Robert Boyle, and with Oldenburg, the Secretary of the Royal Society. With these men he carried on correspondence, and through Oldenburg some letters (the source of 150 years of controversy6) passed between him and Newton. It was during his stay in Paris that he invented the Infinitesimal Calculus, and acquired that breadth of learning, and that acquaintance with the whole republic of letters, which afterwards characterized him. But it was only on his way back from Paris that he learnt to know the greatest man of the older generation. He spent about a month of the year 1676 at the Hague, apparently in constant intercourse with Spinoza; he discussed with him the laws of motion and the proof of the existence of God, and he obtained a sight of part (at any rate) of the Ethics in manuscript7. When the Ethics soon afterwards was posthumously published, Leibniz made notes of it, and undoubtedly bestowed very careful thought upon its demonstrations. Of his thoughts during the years which followed, down to 1684 or even 1686 (since the Thoughts on Knowledge, Truth and Ideas deal only with one special subject), only slight traces remain, and it seems probable that, like Kant in the years from 1770 to 1781, he was in too much doubt to be able to write much. He certainly read Plato8, and he certainly desired to refute Spinoza. At any rate, by the beginning of 1686 he had framed his notion of an individual substance, and had sufficiently perfected his philosophy to send Arnauld what is perhaps the best account he ever wrote of it -- I mean the Discours de Metaphyque (G. IV. 427-463). With this and the letters to Arnauld his mature philosophy begins; and not only the temporal, but the logical beginning also is, in my oplnion, to be sought here. The argument which forms the logical beginning, and gives the definition of substauce, will be found in the four following chapters.
3 See especially Guhrauer, Leibnitz: Eine Biographie, Breslau, 1846; Stein, Leibniz und Spinoza, Berlin. 1890; Selver, Entwicklungsgang der Leibnizschen Monadenlehre, Leipzig, 1885; Tonnies, Leibniz und Hobbes, Phil. Monatshefte, Vol. XXIII.; Trendelenburg, Historische Beitruge, Vol. II., Berlin, 1855.