Jacques Maritain Center : History of Philosophy / by William Turner


If post-Cartesian philosophy is to be described as busying itself with the problem of the antithesis of mind and matter, the pantheistic monism of Spinoza may be designated as an attempt to solve the problem by merging matter and mind in the unity of the infinite substance, and the empirical movement as an attempt to eliminate the antagonism by reducing mind to matter. The idealistic movement, which was represented by Leibniz and Berkeley, was still another essay to remove the antithesis between mind and matter, by reducing matter to mind. Perhaps, however, the true significance of the idealistic movement will be best understood if it is regarded rather as an attempt to restore the aesthetic and religious ideals which were threatened by the first empiricists and destroyed by the atheistic and materialistic empiricists of later times. But, whether we represent the idealistic movement as a solution of the Cartesian problem, or as a reaction against the purely scientific concept of philosophy, it will be evident, in either case, that Leibniz represents a more hesitating and less thorough, while Berkeley represents a more pronounced and more complete, form of idealism.


Life. Gottfried Wilhelm Leibniz was born at Leipzig in 1646. At the age of fifteen he entered the university of his native city, devoting himself to the study of law and philosophy. After obtaining the degree of master of philosophy at Leipzig, and that of doctor of laws at Altdorf, he went to the court of the elector of Mainz, by whom he was sent on a diplomatic mission to Louis XIV of France. In France, England, and Holland he formed the acquaintance of the most learned men of the time, and, with the ample means at his disposal, he had no difficulty in acquiring a wonderfully wide and accurate knowledge of all the scientific and philosophical literature of the day. From 1676 until his death, in 1716, Leibniz resided at Hannover, where he held the offices of court counselor and librarian.

Sources. Leibniz did not compose a complete and extended exposition of his philosophy. His writings are, for the most part, brief treatises and essays on various scientific and philosophical problems. The most important of these are Disputatio Metathysica de Principio Individui, La monadologie, Essais de théodicée, and Nouveaux essais sur l'entendement humain (reply to Locke's Essay). The principal editions of his collected works are those of Raspe (Leipzig and Amsterdam, 1765), Dutens (Geneva, 1768), Erdmann (Berlin, 1840), Foucher de Careil (Paris, 1859 ff.), and Paul Janet (Paris, 1866). Merx's Leibniz (Blackwood's Philosophical Classics, Edinburgh and Philadelphia, 1884) and Dewey's Leibniz's New Essays (Chicago, 1888) will be found useful in the study of Leibniz' philosophy.{1}


General Standpoint. Descartes had started his philosophical speculations with the desire to isolate himself from his fellow-men, and to build up a philosophy which should owe nothing to his predecessors. Leibniz, on the contrary, was inspired with the thought of founding a system which should reconcile all the systems of his predecessors, bring Plato into harmony with Democritus, demonstrate the agreement of Aristotle with Descartes, and prove that there is no inherent contradiction between Scholasticism and modern thought.{2} This was in keeping with the many-sided and cosmopolitan character of the man who, as discoverer of the differential calculus, ranked among the foremost mathematicians of his day, and was equally eminent as a scientist, a philosopher, and a religious controversialist.

With a view to effecting this universal harmony of systems, Leibniz adopted a theory of reality which centers on the doctrine of monads, the principle of preëstablished harmony, and the law of continuity. He sought to establish the perfect correspondence of mind with matter and the participation of matter by mind and of mind by matter (pan-psychism).

Doctrine of Monads. Leibniz, like Spinoza, considers that the notion of substance is the starting point in metaphysical speculation. But, while Spinoza defines substance as independent existence, Leibniz defines it as independent power of action: "La substance ne saurait etre sans action."{3} From this difference there arises another: if substance be defined as self-existence, it is necessarily one, and hence Spinoza was consistent with his definition when he taught that substance is one; whereas, if substance be defined as self-activity, it is essentially individual, and at the same time necessarily manifold. The manifold individual substances are monads.

The monads are analogous to atoms; they are simple, indivisible, indestructible units.{4} They differ from the atoms in this, that no two monads are alike. They differ also in respect to indivisibility; for the atom is not an absolutely indivisible point, while the monad is a metaphysical point, real and indivisible. Finally, they differ from atoms in this, that the atom is merely a material constituent of bodies, whereas the monad is immaterial, in so far, namely, as it is endowed with the power of representation.

This power of representation is the essence, so to speak, of the monad. Leibniz is careful to distinguish between conscious and unconscious representation. Some monads, as for instance the human soul, are conscious of what they represent; others represent unconsciously; each monad, whether consciously or unconsciously, reflects every other monad in the universe. Each monad is therefore a microcosm, a multiplicity in unity, a mirror of all reality, in which an all-seeing eye might observe what is taking place all over the world.{5} One monad differs from another merely in this, that while both represent all reality, one represents it more perfectly than the other. Now, since all the activity of the monad consists in representing, and since there are different degrees in the perfection with which a monad represents other monads, every monad must be dual, partly active and partly passive. Retaining the Aristotelian terminology, while modifying the meaning of the terms, Leibniz calls the passive element the matter, and the active element the form, or entelechy, of the monad. God alone represents all monads with perfect clearness, and is therefore pure actuality; all other monads represent imperfectly, and are therefore partly active (clearly representative) and partly passive (confusedly representative), that is, composed of form and matter. It was thus that Leibniz strove to reconcile the schoolmen with modern thought.

Everything in the universe is composed of monads and everything takes its place in the scale of perfection according to the degree of clearness with which it represents other monads. Every monad is partly material and partly immaterial, so that from the lowest monad, which represents unconsciously, and shows its unconscious perception in the phenomena of attraction and repulsion, up to the highest created monad, which is the human soul, there is absolute continuity without interruption or unnecessary duplication. This is known as the law of continuity.{6} Its counterpart is the law of indiscernibles. If there is no unnecessary duplication, there is no perfect similarity of forms, and, indeed, since no two monads represent the universe in exactly the same manner, no two are perfectly alike. If they were exactly alike they would not be two, but one; for it is the manner of representation that constitutes the individuality of a monad.

Preëstablished Harmony. If each monad is a little universe in itself, reflecting every other monad, and individuated by its manner of representing, if it develops this power from the germs of activity inherent in itself, whence comes the correspondence of one representation with another, and the resulting harmony of the entire system of monads? Leibniz answers by postulating a divine arrangement by virtue of which the monads have from the beginning been so adapted to one another that the changes of one monad, although immanent, are parallel to the changes in every other monad of the cosmic system. This doctrine of preestablished harmony,{7} which is germinally contained in Descartes' doctrine of the relations of the soul to the body, finds its most important application in psychology. Soul and body have no direct influx on each other, but, just as two clocks may be so perfectly constructed and so accurately adjusted that they keep exactly the same time, so it is arranged that the monads of the body put forth their activity in such a way that to each physical activity of the monads of the body there corresponds a psychical activity of the monad of the soul.

When we inquire into the ultimate foundation of this harmony, and look for the reason of the divine arrangement on which the harmony of the universe depends, we find an answer in Leibniz' optimistic principle, the lex melioris. Of possible worlds God chose the best, and, even apart from the divine choice, the best would necessarily prevail over all other possible worlds, and become actual. This lex melioris is itself founded on the law of sufficient reason,{8} that, namely, things are real when there is sufficient reason for their existence. The law of sufficient reason is, according to Leibniz, a law of thought as well as a law of being.

Psychology. From the definition of the monad it is clear that all created reality is partly material and partly immaterial, that there are no bodiless souls and no soulless bodies. Moreover, the law of continuity demands that the soul always think, that reason and sense differ merely in degree, and that sense-knowledge precede rational knowledge. Yet, although the soul, the "queen-monad," is akin to other monads, and although the law of continuity forbids a gap between the soul of man and lower forms, the human soul possesses intellectual knowledge by which it is discriminated from the souls of lower animals. Whence comes this intellectual knowledge? What is the origin of our ideas? In the Nouveaux essais, Leibniz not only contradicts Locke's doctrine that none of our ideas are innate,{9} but lays down the contrary proposition and maintains that all our ideas are innate. He teaches that the soul has "no doors or windows" on the side facing the external world, that, consequently, all our knowledge is developed from germs of thought which are innate. The innateness of our ideas is, however, implicit rather than explicit. Ideas exist potentially in the mind, so that the acquisition of knowledge is the evolution of the virtually existent into the actually existent. To the principle, "Nihil est in intellectu quod prius non fuerit in sensu," Leibniz adds, "nisi ipse intellectus."{10}

Have our ideas, therefore, any objective value? Leibniz answers that they have, because the evolution of the psychic monad from virtual to actual knowledge is paralleled by the evolution of the cosmic monad in the outside world. Here, as elsewhere, the harmony is preëstablished.

The immortality of the soul follows from its nature. The soul is a monad, self-active, self-sufficient (suffisant à lui-même), and is therefore as lasting as the universe itself.

Theodicy. Leibniz' principal treatise on natural theology, the Théodicée,{11} was composed for the purpose of refuting Bayle, who had tried to show that reason and faith are incompatible. The work is devoted, in a large measure, to the discussion of the problem of evil and to the defense of optimism.

Leibniz' arguments to prove the existence of God may be reduced to three: (1) from the idea of God (a modification of Descartes' proof); (2) from the contingency of finite being; and (3) from the character of necessity which our ideas possess. Ideas possess not merely hypothetical but absolute necessity, -- a necessity which cannot be explained unless we grant that an absolutely necessary Being exists.

When it is said that the idea of God plays a teleological rather than a scientific rôle in Leibniz' system of thought, the meaning of this is that Leibniz is interested not so much in giving an account of the origin of the universe, as in discovering an absolute final cause towards which all created being tends. Indeed, we find that the idealist is always more inclined than is the empiricist to fall back on the teleological explanation, and in the philosophy of Leibniz the teleological concept is of especial importance as the foundation of the principle of sufficient reason. It is also of importance as affording a solution of the problem of evil, -- a problem to which Leibniz devoted much attention.{12} He distinguishes metaphysical evil, which is mere limitation or finiteness, physical evil, which is suffering, and moral evil, which is sin. The ultimate source of all evil is the imperfection which of necessity attaches to limited existence, and which therefore must be permitted by God, although it is reduced by Him to the minimum, and made to serve a higher purpose, -- the beauty and harmony of the whole. Leibniz exhorts us to consider evil, not in its relation to parts of reality, but in its relation to the totality of being. "We can see," he writes, "only a very small part of the chain of things, and that part, moreover, which displays the most evil, and which is, therefore, well suited to exercise our faith and our love of God."{13}

Historical Position. The philosophy of Leibniz cannot, like that of Locke, be characterized as superficial. It takes up, and attempts to solve, the most important questions of metaphysics and psychology. In spirit and tone, rather than in method and content, it is Platonic, that is, inspired by idealism and inclined to the poetic rather than to the scientific synthesis. And herein lies its principal defect: it is unreal. For although Leibniz was as fully alive as was any of his contemporaries to the importance of scientific study and experimental investigation, his philosophy is built, not on the data of experience, but on a priori definitions and principles. Yet we must not on this account underrate the importance of Leibniz as a speculative thinker. He rendered inestimable service to the cause of philosophy by setting himself in determined opposition to the current of empirical sensism. Besides, the study of his philosophy is healthful; it expands the mind, opens up new vistas of philosophic syntheses, and is an invaluable aid to the understanding of subsequent systems.

In the philosophy of Berkeley we find another phase of idealism, an idealism carried to the point of the absolute denial of the reality of matter.


Life. George Berkeley was born at Dysert, in County Kilkenny, Ireland, in the year 1685. After having made his elementary studies at Kilkenny, he went, in 1700, to Trinity College, Dublin, where, owing to the influence of Molyneux, the philosophy of Locke was in the ascendency. From the Common-place Book, in which, as early as 1705, Berkeley began to set down his thoughts on philosophical problems, it appears that, while still at Trinity College, he had begun to study Descartes and Malebranche as well as Locke. In 1709 he published his New Theory of Vision, and in the following year, his Principles of Knowledge. In 1713 he went to London, where he formed the acquaintance of Steele, Collins, Swift, Pope, and Addison, and in the winter of the same year he visited Père Malebranche at Paris. After several years spent in France and Italy, he returned to London in 1720, to find the whole country in a turmoil over the failure of the South Sea Scheme. It was this condition of affairs that prompted Berkeley to write his Essay towards Preventing the ruin of Great Britain. In 1721 he returned to Ireland to receive a deanery in the Established Church. From 1723 until 1731 he was occupied with his famous scheme for converting the American Indians and with the project of founding for that purpose a college in Bermuda. The two years which he spent at Whitehall, near Newport, Rhode Island, while waiting for the government grant promised by Sir Robert Walpole, afforded him an opportunity to continue his philosophical studies and to make the acquaintance of Samuel Johnson, through whom he may be said to have influenced Jonathan Edwards, the first representative of philosophy in America. On returning to London in 1731, Berkeley published his Alciphron, or the Minute Philosopher, a dialogue directed against the freethinkers (minute philosophers). In 1734 he was made bishop of Cloyne, in Cork. In that "serene corner" he combined the study of Plato with the advocacy of tar water as a cure for all human ills, publishing Siris; A Chain of Philosophical Reflections and Inquiries concerning the Virtues of Tar Water, etc. In 1752 he went Oxford, where he died in the following year.

Sources. Berkeley's most important works are An Essay toward a New Theory of Vision, A Treatise concerning the Principles of Human Knowledge, Three Dialogues between Hylas and Philonous, Alciphron, or the Minute Philosopher, the Analyst, and Siris. The best edition of his collected works is Fraser's (4 vols., Clarendon Press, 1871, new edition, 1901). Fraser's Berkeley (Blackwood's Philosophical Classics, Edinburgh and Philadelphia, 1894) is an excellent introduction to the study of Berkeley and his philosophy.{14}


General Aim of Berkeley's Philosophy. In the Common-place Book, of which mention has already been made, we find the following entry: "The chief thing I do, or pretend to do, is only to remove the mist and veil of words." The great obstacle to the discovery and acceptance of truth is, Berkeley thinks, the use of words which represent abstractions of the mind and prevent us from arriving at a knowledge of "things." Locke had indeed announced the principle that our knowledge extends only to ideas; but he straightway proceeded, Berkeley observes, to violate this very principle when he maintained that we know the qualities and powers of things outside the mind and have a "sensitive knowledge of their existence. Berkeley, therefore, starts where Locke had started, but he aims at going farther than Locke had gone, -- at establishing the truth of the conclusion that "all things are ideas," a conclusion which Berkeley regards as necessarily involved in Locke's principle that our knowledge extends to ideas only.

Immaterialism. In his New Theory of Vision, Berkeley takes the first step in the direction of immaterialism. He shows, in the first place, that the only phenomena which we perceive by means of sight are colors, and that with these we associate the phenomena of touch and muscular movement. He then proceeds to show that the reason of the association is "custom," "experience," or "suggestion." The conclusion is that what we "see" in the world around us is far more dependent on mind than we are commonly aware of.

In the Treatise concerning the Principles of Human Knowledge, he takes up once more the problem of knowledge, and endeavors to show that what he had proved to be true of the phenomena of sight is true of the whole phenomenal world of sense; he tries, moreover, to find the reason for the custom, experience, or suggestion, by virtue of which we associate certain phenomena with certain others. He teaches that all the qualities of matter, primary as well as secondary, resolve themselves into mind-dependent phenomena. What, then, is it that groups these phenomena, for example, the color, size, shape, etc., of an orange, into those clusters or aggregates which we call "things"? The answer that phenomena are grouped together by an inert, lifeless matter is self-contradictory, because phenomena, being essentially mind-dependent ideas, cannot exist in an unperceiving substance.{15} Besides, matter is a mere abstraction, one of those words which merely serve to throw a "veil and mist" between the mind and a knowledge of truth. It is evident, therefore, that both the popular and the philosophical conceptions of matter are absurd. There is no material substratum of things; mind and mind-dependent phenomena alone exist; to be is to be perceived, -- esse est percipi.

Yet the world is not a chaos, but a cosmos: there is a continual change and succession of phenomena, and in all this change and succession there is order and regularity. "There is, therefore, some cause of these ideas, whereon they depend. . . ,but it has been shown that there is no corporeal or material substance: it remains, therefore, that the cause of ideas is an incorporeal substance or spirit."{16} Now, since the ideas actually perceived sense have no dependence on my will, it follows that it is not ny mind but the eternal, uncreated spirit that produces them.{17}

Matter does not exist: spirit exists; the "external world" is spirit and the phenomena which spirit produces in the created mind; the only noumenal realities are God and human minds, -- these are the conclusions in which Berkeley's immaterialism is summed up. It follows that there are no secondary causes and that the laws of nature are really laws of the Eternal Spirit.

Theism. In the Dialogues, and especially in the Alciphron, Berkeley undertook to show what is meant by the Eternal Spirit, to Whom he had, in his earlier treatises, referred the persistence and activity of the phenomena into which he bad analyzed the "external world." His line of reasoning may be described as analogical: just as we "see" men we "see" God. As we argue from the phenomena of sight, hearing, etc., to the existence of the human spirit in men, so we may argue from the phenomena of sense in general to the existence of the Infinite Spirit Whose thoughts (physical laws) are conveyed to us in the language of sense phenomena (physical qualities). Alciphron, the sceptic, confesses, "Nothing so much convinces me of the existence of another person as his speaking to me." To which Euphranor replies, "You have as much reason to think the Universal Agent, or God, speaks to your eyes as you can have for thinking any particular person speaks to your ears."{18}

Platonism. The study of Plato, which, during his residence at Cloyne, Berkeley combined with the study of the medicinal properties of tar water, developed in the mind of our philosopher a growing tendency towards a mystic view of the problem of the ultimate reality of things. In the metaphysical portion of the Siris, which he published at this time, he occupies himself with the problem of showing how we may arrive at a higher knowledge of God than that afforded by sense-phenomena. In his Dialogues he was satisfied with refuting atheism by showing how God speaks to us in nature, but now he seeks a higher and deeper knowledge. The study of Plato has led him to the realization of the "uncertain, ever-fleeting, and changing nature" of sensible things, and to the consequent depreciation of sense-knowledge as being "properly no knowledge, but only opinion."{19} Therefore he counsels the seeker after truth to cultivate the use of intellect and reason; to penetrate, by the exercise of these faculties, to a knowledge of the inner nature of things; and through rational faith in causality, to realize that "there runs a chain throughout the whole system of beings," and that, by ascending from what is lower to what is higher, the mind may reach a knowledge of the Highest Being. This is a lifelong task. "He that would make a real progress in knowledge must dedicate his age as well as his youth, the later growth as well as first fruits, at the altar of Truth."

Historical Position. It was Berkeley's intention to remove "the mist and veil of words," and then from empirical principles to refute materialism and atheism. If matter does not exist, there is certainly no justification for materialism, and if all our ideas are produced in us by the Eternal Spirit, if every act of knowledge implies the existence of God, then atheism is undoubtedly irrational and untenable. Berkeley had not the least suspicion of the facility with which scepticism would take advantage of his immaterialism to reason away spirit as he himself had reasoned away material substance. "You see," says Philonous at the end of the third dialogue, "the water in yonder fountain; how it is forced upwards in a round column to a certain height, at which it breaks and falls back into the basin whence rose; its ascent as well as descent proceeding from the same uniform law or principle of gravitation. Just so, the same principles which, at first view, lead to skepticism, pursued to a certain point, bring men back to common sense."{20} However, Berkeley built less wisely than he knew. He carried the principles of empiricism and idealism to a certain point, -- it is commonly said that he is to Locke what Spinoza is to Descartes, -- but at that point they were taken up by Hume and carried their logical conclusion, namely pan-phenomenalism.

{1} For summary of Leibniz' doctrines, cf. Brucker in preface to Duten's edition of Leibniz' works (Leibnitii Opera Omnia, Geneva, 1768, Vol. I, pp. 143 ff.). Consult article on Leibniz in Encyc. Brit.; also Thilly, Leibnizens Streit gegen Locke, Heidelberg, 1891.

{2} Cf. Fouillée, Histoire de la Philosophie (Paris, 1891), p. 306.

{3} Cf. Opera, I, 733, and II, P. II, 19.

{4} Cf. op. cit., II, P. I, 22ff. {5} Cf. op. cit., II, P. I, 33.

{6} Cf. op. cit., I, 366.

{7} Cf. op. cit., II, P. I, 24, 40, 65.

{8} Cf. op. cit., I, 152.

{9} Nouveaux essais, Preface.

{10} Cf. op. cit. II, 1.

{11} In Duten's edition, I, 117 ff., Tentamina Theodiceae de Bonitate Dei Libertate Hominis et Origine Mali.

{12} Cf. Opera, I, 478 ff.

{13} Letter to Bourguet, quoted by Höffding. op. cit., I, 366.

{14} Consult also Fraser's Selections from Berkeley (fourth edition, London, 1891) and Simon, Universal Immaterialism (London, 1862).

{15} Works, I, 142. References are to Fraser's edition (Clarendon Press, 1871).

{16} Op. cit., I, p. 169.

{17} Op. cit., I, p. 172.

{18} Op. cit., II, 146 ff.

{19} Op. cit., II, 482.

{20} Op. cit., I, 360.

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