From London Leibuitz returned to Hanover, where he was engaged in arranging the library and in the discovery and development of the method of infinitesimal!, which was so similar to the method of fiuxions of Newton as to lead to a bitter dispute between the admirers of there great men, and ultimately between themselves, as to the priority of discovery. To decide this dispute the Royal Society of London, at the request of Leibnitz, nominated a commission, which decided in favour of Newton. There is little doubt however that the two methods were equally independent and original ; but the priority of publication is in favour of Leibnitz. To this period belong also the important works of a mixed historical and political nature, Scriptorei Reruns Brunsvicensium,' and the 'Codes. Juris Gentium Diplomatious,' the materials of which he had collected during his travels through France, Suable, Bavaria, and Austria, which ho under took at the instance of Duke Ernest Augustus of Brunswick. In 1693 he joined Otto Menace in publishing the Acta Eruditorum ' of Leipzig, and from 1691 he was also a constant contributor to the 'Journal des Sevens,' in which many of his most important eager on philosophy first appeared. To this period belong the composition of the 'Monadologie' and the 'Harrnonie Predtablie.' Iu 1702 Leibnitz was appointed President of the Academy of Sciences at Berlin, which the Elector of Brandenburg, afterwards Frederick I. of Prussia, had established at the instance of his queen, a princess of the house of Brunswick, and by the advice of Leibuitz himself. In 1710 the Theedic6e' was published, with a view to oppose the tendency of the writings of Boyle; and two years afterwards the Nouveaux Easels cur rEntendernent liumain,' in answer to the essay of Locke. In the previous year Leibnitz formed the personal acquaintance of Poter the Great, who, at Torgau, consulted him on the beat means to be adopted for the civilisation of Russia, sod rewarded his valuable suggestions by the title and dignity of councillor of state and a pension of 1000 rubles. Shortly afterwards, at the instance of Prince Ulrich of Brunswick, the emperor, Charles VL, elected him aulic councillor and baron of the empire; and, in consequence, he visited Vienna, where be became acquainted with the Prince Eugene of Savoy and the chancellor Couut Sinzendorf. Upon the elevation of the Elector of Hanover to the throne of England, Leibnitz returned to Hanover, where, after the publication of a few political and philosophical works, he expired on the 14th of November 1714. He was buried ou the esplanade at Leipzig, where a monument in the form of a temple indicates, by the simple inscription, " Ossa Leibnitii," the place of his buriaL The first objeot of the philosophical labours of Leibnitz was to give to philosophy the rigour and stability of mathematical science. The latter derives this character both from its formal portion, or demon stration, and also from tho nature of Its objeot-matter. With a view to tho former, Leibnitz assumed the existence of certain universal and necessary truths which are not derived from science, but grounded in the very nature of the thinking soul. (' Principia Philosophia,' a. 30.7.) As the objeot-matter of mathematics may be supposed tu be con structed of points or units, Leibuitz was led to the assumption of certain primary constituents of all matter. These are his fatuous mounds, which form the basis of his system. These mounds are simple substances without parts, out of which all bodies are corn pounded by aggregation. They aro real, because without real simple principles the composite would not poeseas reality ; and consequently, if there were uo monads, nothing of any kind could exist really. These monads must not be confounded with the atoms of Democritus or Epicurus. They are real unite, the grouuds of all activity, or forces, and the prima absolute principles of all composite things, which may ultimately bo resolved into them. Leibnitz called them metaphysical points and substantial forms. Being without parte, they are necessarily unextended, indivisible, and without figure. As such they are incapable of dissolution, and without natural decay or pro duction, which is only possible in composite bodies. The monads therefore were created at once and momentarily, and in the mule manner they must be destroyed or last for ever. Internally they admit not of change, since neither substance nor accident can pene trate what is wholly without parts. Nevertheless they must possess certain determinations or qualities, since otherwise they could not be things. Further, every monad is distinct from all others; for there cannot bo two things absolutely ideutical and without internal differ ence. This proposition forms one of Leibnitz's necessary and funda mental principles, which he called the " principle of identity of indisceruibles" (principium identitatis indiaccruibilium). According to this principle all thiugs must differ more or less, since otherwise they would be indistinguishable, for identical things are iudiscernible. All created things are subject to change; consequently the monads also are constantly changing. This change however is only external, end does not operate internally; on the contrary, the outward change results from an internal principle; and this internal principle of change constitutes the essence of all force : the monads consequently are forces. Besides this principle of change, every monad possesses also a certain schema of that which is changed, which, so to say, while it espreeses the differences and multiplicity of the monad, yet comprises the multiplicity in unity. All natural changes proceed in gradatiou ; consequently, while ouo part is changing, another remains unchanged, and tho monads cousequently possess a plurality of affections and relations. This traueitory state, which experiences and exhibits tho multiplicity of changes in the unity of the monad, is perception, which however is unconscious (sine conscientia). The active force, by which the change or passage from perception to perception is accom plished, is an appetite (appetitus). By its action the monads are ever attaining to new perceptions, in which their whole activity consists, and besides which nought else is in them ; consequently they may be termed entelechies, as possessing a certain perfection and a certain self-sufficiency by which they are the sources of their own activity. In lifeless things perception is uncombined with consciousness; in animated, it is combined with it and becomes apperception. The monads endued with apperception may be called souls, and, in combi nation with the unconscious monads, constitute all animals; the only difference between man and the rat of animals, as between God and man, consisting in a higher degree of perfection. The unconscious perception is also found in the monads endued with apperception, when they are in a state of sleep or are stunned, for in sleep the soul is without apperception, and like the other monads. All perceptions however are closely dependent on each other; and when consequently the soul passes from sleep, the unconscious perceptions which it had during that state form the link which connects its present thoughts with the past. This fact affords an explanation of memory, and that anticipation of like results from like causes which guides the conduct of all animals. Alan however is distinguished from the rest by his
cognition of eternal and necessary truths; by these he rises to a know ledge both of his own and the Divine nature; and these constitute what is called reason or mind. By these necessary truths man becomes capable of the reflex art of distinguishing the subject (ego) and the object (res), and furnishes him with the fundamental princi ples of all reasoning, namely, the principle of contradiction and the law of sufficient reason. According to the former, whatever involves a contradiction is false, and its opposite true; the latter teaches that nothing can be true or exist unless some reason exist why it should be as it is, and not otherwise. This sufficient reason of all necessary truths may be discovered by analysis, which arrives ultimately at the primary notions which assume the form of identical propositions, and are incapable of proof, but legitimate themselves. In the same manner all contingent truths must have an ultimate cause, since otherwise an infinite series of contingencies must be assumed in which reason would be lost. This last cause of all things and of their mutual dependence in the universe is God, who is absolute infinite perfection, from whom all things derive their perfection, while they owe their imperfection' to their own nature, which, as finite, is incapable of receiving into itself infinite perfection. The Divine intellect is also the source of all eternal truths and ideas, and without God nothing could possibly be actual, and nothing could exist necessarily. God alone, as possessing infinite perfection, exists of necessity ; for as nothing obstructs his potentiality, he is without negation or contra diction, and is unlimited. But although the eternal truths have their reason in the nature of God, they are not therefore arbitrary or deter mined by the will of God. This is the case only with contingent truths. God, as the prime monad by whom all created monads were produced, is omnipotent; as the source of the ideas after which all things were created and from which they receive their nature, he is intelligent, and he also possesses a will which creates those finite things which his intelligence recognises as the best possible. These same properties of intelligence and will constitute the subject, or ego, in man, by which he is capable of perceiving or desiring. While how ever these attributes are in the highest degree of perfection in the Deity, in finite things they are variously limited, according to the respective degrees of perfection.
As imperfect, the activity of the created monads tends without themselves ; consequently they possess activity so far as they possess clear perceptions (apperception), and are passive so far as they perceive obscurely. Of two composite substances, that is the more perfect which possesses the ground of the contingent changes of the latter : but simple substances cannot exert any influence on each other, unless by the intervention of the Deity, who at the creation arranged them in due co-ordination with each other. This adjustment of the monads was in accordance with certain sufficient reasons in each monad, by which the Divine will was moved to place the passivity of ono and the activity of one in an harmonial relation ; this sufficient reason was their comparative perfection : hence the famous principle of Leibnitz, which has been designated by the term Optimism—that of all possible worlds, God has chosen and produced the best.
As every monad stands in harmonious relation to all others, it expresses the relations of all, and is, as it were, a mirror of the uni verse which is represented in a peculiar manner by each. Hence the greatest possible variety is combined with the greatest possible harmony. God alone can embrace all these relations, while finite minds have only a very obscure perception of them. All in the world is full, and bound together into one continuous and coherent whole. The motion of each single monad, whether simple or in aggregation, affects all according to distance; and God therefore sees all future things, as well as present and past. But the soul is only cognisant of what is present to it; and although indeed It represents the whole universe, yet the infinity of objects surpasses its capacity, and its clearest representations are of those which immediately affect the body with which it is united. The soul pursues its own laws, and the body likewise its own ; both however, by reason of the harmony established at the creation among all monads, as representatives of the universe, act in unison. The soul strives after means and ends, and works by the laws of final causes; the body, by those of efficient causes. Both species of causes are in harmony with each other. Such is the system of pre-established harmony, according to which the body and soul act independently of each other, and each as if the other did not exist, and yet nevertheless both as if they had an influence on each other. This harmonious relation of the body and soul Leibnitz illustrates by the supposition of two clocks, one of which points, while the other strikes the hour : both harmonise in their movements, but nevertheless are independent of each other.
The power and goodness of God are displayed in the whole universe, but it is in the moral world that they are chiefly visible. Between the natural and the moral worlds, or between God as creator of the mundane machine and as ruler of spirits, the strictest harmony sub sists. God as architect of the world is consistent with himself as lawgiver; and agreeably to the mechanical regulation of the course of nature, every transgression is followed by punishment, as every good act is by rewards, since all is so disposed as to contribute to the good and happiness of the whole. This is the grand principle of the Theodicee.' In this work Leibnitz shows that God, as all-powerful, all-wise, and all-good, has chosen and created the best of all possible worlds, notwithstanding the seeming objections which may be drawn from the existence of evil. If a better constitution of things had been possible, God would have chosen it in preference; and even if another equally good had been possible, there would not have been any suffi cient reason for the existence of the present world. The existence of evil is both metaphysical and physical. As to the former, the ante cedent will of God designed infinite good; but this was not possible, since the multiplicity of things necessarily limit each other, and this limitation is evil. But evil may also be oonsidered as physical and moral. Physical evil is a necessary consequence of the limitation of finite things. Moral evil however was not necessary, but became a consequence of metaphysical and physical. But the less evil must be admitted for the sake of greater good; and evil is Inseparable from the best world, as the sum of finite beings to whom defect and imper fection necessarily cling by nature. God therefore permitted its existence : for as the world contains a good incomparably greater than its attendant evil, it would have been inconsistent with the Divine goodness and wisdom not to have realised the best possible world, in consequence of tho comparatively little evil which would come into existence with it.