The historical importance of Leibniz's ideas is anyhow unmistakable. If metaphysical thinking is nonsensical, its empire over the human imagination must still be confessed; if it is as chimerical a science as alchemy, it is no less fertile in by-products of importance. And if we are to consider Leibniz historically, we cannot do better than take up his Theodicy, for two reasons. It was the only one of his main philosophical works to be published in his lifetime, so that it was a principal means of his direct influence; the Leibniz his own age knew was the Leibniz of the Theodicy. Then in the second place, the Theodicy itself is peculiarly rich in historical material. It reflects the world of men and books which Leibniz knew; it expresses the theological setting of metaphysical speculation which still predominated in the first years of the eighteenth century.
Leibniz is remembered for his philosophy; he was not a professional philosopher. He was offered academic chairs, but he declined them. He was a gentleman, a person of means, librarian to a reigning prince, and frequently employed in state affairs of trust and importance. The librarian might at any moment become the political secretary, and offer his own contributions to policy. Leibniz was for the greater part of his active life the learned and confidential servant of the House of Brunswick; when the Duke had nothing better to do with him, he set him to research into ducal history. If Leibniz had a profession in literature, it was history rather than philosophy. He was even more closely bound to the interests of his prince than John Locke was to those of the Prince of Orange. The Houses of Orange and of Brunswick were on the same side in the principal contest which divided Europe, the battle between Louis XIV and his enemies. It was a turning-point of the struggle when the Prince of Orange supplanted Louis's Stuart friends on the English throne. It was a continuation of the same movement, when Leibniz's master, George I, succeeded to the same throne, and frustrated the restoration of the Stuart heir. Locke returned to England in the wake of the Prince of Orange, and became the representative thinker of the régime. Leibniz wished to come to the English court of George I, but was unkindly ordered to attend to the duties of his librarianship. So he remained in Hanover. He was then an old man, and before the tide of favour had turned, he died.
Posterity has reckoned Locke and Leibniz the heads of rival sects, but politically they were on the same side. As against Louis's political absolutism and enforced religious uniformity, both championed religious toleration and the freedom of the mind. Their theological liberalism was political prudence; it was not necessarily for that reason the less personally sincere. They had too much wisdom to meet bigotry with bigotry, or set Protestant intolerance against Catholic absolutism. But they had too much sympathy with the spirit of Europe to react into free thinking or to make a frontal attack on revealed truth. They took their stand on a fundamental Christian theism, the common religion of all good men; they repudiated the negative enormities of Hobbes and Spinoza.
The Christian was to hold a position covered by three lines of defences. The base line was to be the substance of Christian theism and of Christian morals, and it was to be held by the forces of sheer reason, without aid from scriptural revelation. The middle line was laid down by the general sense of Scripture, and the defence of it was this. 'Scriptural doctrine is reconcilable with the findings of sheer reason, but it goes beyond them. We believe the Scriptures, because they are authenticated by marks of supernatural intervention in the circumstances of their origin. We believe them, but reason controls our interpretation of them.' There remained the most forward and the most hazardous line: the special positions which a Church, a sect, or an individual might found upon the scriptural revelation. A prudent man would not hold his advance positions in the same force or defend them with the same obstinacy as either of the lines behind them. He could argue for them, but he could not require assent to them.
One cannot help feeling, indeed, the readiness of these writers to fall back, not only from the front line to the middle line, but from the middle line itself to the base line. Leibniz, for example, writes with perfect seriousness and decency about the Christian scheme of redemption, but it hardly looks like being for him a crucial deliverance from perdition. It is not the intervention of Mercy, by which alone He possesses himself of us: it is one of the ways in which supreme Benevolence carries out a cosmic policy; and God's benevolence is known by pure reason, and apart from Christian revelation.
In one politically important particular the theological attitude of Leibniz differed from that of Locke. Both stood for toleration and for the minimizing of the differences between the sects. This was a serious enough matter in England, but it was an even more serious matter in Germany. For Germany was divided between Catholics and Protestants; effective toleration must embrace them both. English toleration might indulge a harmless Catholic minority, while rejecting the Catholic régime as the embodiment of intolerance. But this was not practical politics on the Continent; you must tolerate Catholicism on an equal footing, and come to terms with Catholic régimes. Leibniz was not going to damn the Pope with true Protestant fervour. It was his consistent aim to show that his theological principles were as serviceable to Catholic thinkers as to the doctors of his own church. On some points, indeed, he found his most solid support from Catholics; in other places there are hints of a joint Catholic-Lutheran front against Calvinism. But on the whole Leibniz's writings suggest that the important decisions cut across all the Churches, and not between them.
Leibniz was impelled to a compromise with 'popery', not only by the religious divisions of Germany, but (at one stage) by the political weakness of the German Protestant States. At the point of Louis XIV's highest success, the Protestant princes had no hope but in Catholic Austria, and Austria was distracted by Turkish pressure in the rear. Leibniz hoped to relieve the situation by preaching a crusade. Could not the Christian princes sink their differences and unite against the infidel? And could not the Christian alliance be cemented by theological agreement? Hence Leibniz's famous negotiation with Bossuet for a basis of Catholic-Lutheran concord. It was plainly destined to fail; and it was bound to recoil upon its author. How could he be a true Protestant who treated the differences with the Catholics as non-essentials? How could he have touched pitch and taken no defilement? Leibniz was generally admired, but he was not widely trusted. As a mere politician, he may be judged to have over-reached himself.
It has been the object of the preceding paragraphs to show that Leibniz the politician and Leibniz the theologian were one and the same person; not at all to suggest that his rational theology was just political expediency. We may apply to him a parody of his own doctrine, the pre-established harmony between nature and grace. Everything happens as though Leibniz were a liberal politician, and his theology expressed his politics. Yes, but equally, everything happens as though Leibniz were a philosophical theologian, and his politics expressed his theology. His appreciation of Catholic speculation was natural and sincere; his dogmatic ancestry is to be looked for in Thomism and Catholic humanism as much as anywhere. Above all, he had himself a liberal and generous mind. It gave him pleasure to appreciate good wherever he could see it, and to discover a soul of truth in every opinion.
From the moment when Leibniz became aware of himself as an independent thinker, he was the man of a doctrine. Sometimes he called it 'my principles', sometimes 'the new system', sometimes 'pre-established harmony'. It could be quite briefly expressed; he was always ready to oblige his friends with a summary statement, either in a letter or an enclosed memorandum, and several such have come down to us. The doctrine may have been in Leibniz's view simple, but it was applicable to every department of human speculation or enquiry. It provided a new alphabet of philosophical ideas, and everything in heaven and earth could be expressed in it; not only could be, but ought to be, and Leibniz showed tireless energy in working out restatements of standing problems.
As a man with an idea, with a philosophical nostrum, Leibniz may be compared to Bishop Berkeley. There was never any more doubt that Leibniz was a Leibnitian than that Berkeley was a Berkeleian. But there is no comparison between the two men in the width of their range. About many things Berkeley never took the trouble to Berkeleianize. To take the most surprising instance of his neglect—he assured the world that his whole doctrine pointed to, and hung upon, theology. But what sort of a theology? He scarcely took the first steps in the formulation of it. He preferred to keep on defending and explaining his esse est percipi. With Leibniz it is wholly different; he carries his new torch into every corner, to illuminate the dark questions.