Leibniz propounds a pluralistic metaphysical idealism by reducing the reality of the universe to centres of force, which are all ultimately spiritual in their nature. Every centre of force is a substance, an individual, and is different from other centres of force. Such centres of force, Leibniz calls monads. These forces are unextended, not subject to division in space. None, excepting, of course, God, can destroy these monads, and so they are considered to be immortal in essence. Though quantitatively, the monads are practically similar to one another, qualitatively they are different. As the monads are spiritual entities, their internal differences too are determined by a spiritual character. It is this difference among them that gives them their distinctive individuality. We are reminded here of the viseshas, or differentia, of the ultimate atoms in the Nyaya and Vaiseshika philosophies, the viseshas giving a distinctive individuality to the atoms. The monads of Leibniz are subject to the changes of perception and appetition, each monad striving to attain clearer and clearer perception, which process is an attempt of the monad to come to a consciousness of greater and greater perfection in itself. The manifoldness of the monads and the way in which they are arranged account for the diversities of the world. These monads are present everywhere in the universe - in man, animal, plant and even in inanimate matter. For Leibniz there is no dead matter or blind force. Matter is endowed with life through and through. As all monads are not of the same kind, they admit of a hierarchy of degrees among themselves. There is a rise in the consciousness of perfection from matter to man. In matter the monads are unconscious; in man they rise to reflective consciousness.

Every monad is like a mirror, which reflects in itself the entire universe. A universal situation can be seen represented in a monad. The degrees of clarity in which the monads reflect the universe in themselves differ according to the position which they occupy in the great hierarchy, which, again, is determined by the degree of the clarity of their perception. Their positions are determined by the intensity and clearness of their consciousness. The higher ones are considered to be the images of God, and the lower ones mirrors of the universe. Though the monads have this capacity, they are by no means infinite, for outside them there are other monads. Leibniz tells us that the past, present and future of things can be seen in a single monad; the knowledge of the constitution of a monad would give us a knowledge of the whole universe. In the hierarchy of monads there are infinite degrees, from the lowest to the highest, a gradually ascending series of spiritual entities or forces with no jumps or leaps of any kind between one monad and another. God is the highest Monad. Leibniz proves the existence of God in five ways: by the ontological proof, the cosmological proof in terms of the law of sufficient reason, the teleological proof, proof by the law of pre-established harmony, and the epistemological proof which requires a background for the eternal necessary truths seen in the world.

Like the entelechies of Aristotle, the monads of Leibniz are directed by an inner necessity, and not by outward compulsion. It is to be remembered that these monads are windowless essences, not permitting in the entrance of anything from outside. One monad cannot influence the other. True knowledge is infinite, unfolded from within, not received from outside. The possibilities of a monad are hidden in it, as a tree is latent in a seed. Evolution is the process of the realisation of the inner potentialities of the monads. The higher stages of evolution include and transcend the lower ones. The whole life of a monad is therefore a long chain with many links of the stages of self-transcendence. The past is over-stepped in the present and the present transcended in the future. We have again the reminiscences of Aristotle in the view of Leibniz that the succeeding stages in the evolution of a monad are the results or effects of its preceding stages, so that no action from above or outside is necessary for its evolution. Though one monad is different from the other, each monad bears a harmonious relation to all the other monads. We may notice here the germs of the philosophy of organism brilliantly expounded later by Whitehead. Leibniz tries to bring about a reconciliation between mechanism and teleology by holding that insofar as the physical realm is governed by strict law and order, it can be explained mechanically, but that the scheme of the universe is directed by a final aim towards which it evolves. Mechanics, for Leibniz, is rooted in metaphysics; the mathematical and mechanical laws of the physical realm point to God as their ultimate goal. Science and religion are thus brought together. We get an organic whole of a universe where every fact or event had a reason why it exists or happens in such and such a manner, in such a place and at such a time. Not only should every judgment have a reason to prove it, but every object a reason to be. This is the law of sufficient reason advocated by Leibniz, which is at once logical as well as metaphysical. This law leads to a kind of determinism rather than to give room to free-will, for the causes of an event or a fact are determined already by the circumstances in which a monad is placed in the hierarchy, and even an apparent free choice would only be the result of the joint action of the various conditions, the contingent past and present factors, which make the monad what it is. But Leibniz allows some free-will without properly explaining how this is to be reconciled with the absolute supremacy and omnipotence of God. The law of sufficient reason requires the universe to be a rational whole, where logical and metaphysical truths become identical.

The individual souls which form a divine hierarchy of monads have much in common with God who is their prototype. The reason in man is essentially one with God's consciousness, but it differs from the latter in the degree of its intensity. The kingdom of God has therefore two aspects: the hierarchy of monads and the physical universe. All these work together parallelly by pre-established harmony. The same old parallelism in the workings of the mind and the body persists with a different note in the philosophy of Leibniz. God, according to Leibniz, has arranged the mind and the body in such a way that the two work in harmony with each other. God has endowed all monads with identical contents. The theory of windowless monads prevents any interaction among them. The harmony of functions between the psychic and the physical states is pre-established by God, in the beginning. Though the monads have different kinds of perception, there is a single current underlying them all. Minds and bodies form parts of the organism of the universe. Though the parts of the organism are connected by causal relations, it should not be forgotten that these relations are strictly preordained by God and are not to be understood in the sense of actual interaction.

There is a difference in the manner of action in souls and bodies. Souls are directed by a teleological law; bodies are determined by mechanical motion. But both work in unison by pre-established harmony. Leibniz also adds that the spiritual monads, when they are perceived by the senses, appear as the phenomenal universe; in other words, matter is spirit discerned by the senses.

God, Who is the highest Monad, is changeless and has no modification. He is the absolutely real being. But the great importance which Leibniz gives to logic and mathematics, considering them to be examples of eternal truths, makes him think that the laws of human thought are binding on God, also.

Leibniz holds that there are monads within monads. There are organisms living even in what is ordinarily supposed to be dead matter. Every particle of matter houses several living organisms. Every such organism, again, is an abode of several other organisms, and so on. His theory of the universal presence of living beings is called panpsychism.

The relation between God and the monads Leibniz speaks of in different ways. Sometimes he thinks that they are eternal, sometimes that they are created by God, Who can even destroy them, if He wills, and sometimes that they are manifestations of God Himself. If they are eternal, they must be different from God and have nothing to do with God, in which case they cannot reach the perfection of God. Further, as they are limited entities, they cannot be eternal. If they are not eternal, they must be perishable and have no real worth in them. If their goal is God, God must be immanent in them; in other words, they must be God Himself appearing, and not entities created by God Who can even destroy them. The monads are either existent or non-existent. If they are existent, they are real, and so cannot be destroyed; if they are non-existent, there is nothing to be destroyed.

The plurality of monads in the system of Leibniz is a great hindrance to a satisfactory explanation of their relation to God. If they are really plural in their essence, they will become independent eternal entities, whose eternity would only be in name. For, there cannot be eternity of many things; individuality is subject to spatiality, and so to change. Leibniz is anxious to make the universe a harmonious whole, but this he does with a highly artificial scheme of pre-established harmony. This pre-establishment cannot be established without the doctrine of the plurality of monads, which, again, cannot be established without pre-established harmony. The reasoning becomes circular. That there is interaction between mind and body and between individuals cannot be doubted. Much later, Whitehead made it clear that every entity in the universe flows into every other and that there are no watertight compartments among things. Moreover, if the monads are different from one another, they would have to be contained in space, for we cannot have the notion of difference without the notion of space. But for Leibniz the monads are immaterial and unextended. If they are extended in space, they are material bodies; if they are unextended and spiritual, there cannot be a plurality of them. Only a universal, undivided wholeness, where plurality is transcended, can justify the spirituality of the monads. Else, they would be reduced to physical atoms hanging in space.

In the philosophy of the Vedanta, the plurality of ultimate substances has no place. It admits that there is a plurality of Jivas, or individual souls, but these are not the ultimate essences of existence. The essence of the Jiva is the Atman, which is pure consciousness in nature. There is no plurality of Atmans; the Atman is one in reality and it is identical with God, or the Absolute. We notice a confusion in Leibniz between minds and souls. The Vedanta makes a distinction between the mind and the soul. The soul, in the sense of Jiva, is a manifestation of the Supreme Atman through the medium of the mind. The mind is as much physical as the body, though much subtler and more transparent than the latter. In this sense there can be a plurality of individual souls, but not of ultimate essences or realities. A plurality of realities would make the realities individual beings and consequently transient in nature. If the monads of Leibniz are distinguishable individualities, they cannot be eternal and immortal. If Leibniz means by his monads minds and not spiritual essences in the sense of the Atman, the Vedanta would agree with Leibniz that the monads are many. But as ultimate realities they cannot be so, for reality can only be one. Plurality is impossible without spatiality, and reality is above space.

Leibniz seems to think that the monads may even be destroyed by God. This is a great self-contradictory view held by him, for what is subject to destruction cannot be immortal; immortality implies eternal existence. What is eternal cannot be an effect or product of something else. Eternity does not begin somewhere in time. Naturally, the uncreated which should, at the same time, be non-spatial, has to be identified with the ultimate reality, which is God. Destruction in the sense of transformation of state may be brought about by God in regard to phenomenal objects, but not immortal beings like the monads of Leibniz. The Jivas, on the other hand, are essentially indestructible beings, though their relative constitutions may undergo change in the process of evolution. Even here it is the psychic or mental body which constitutes the Jivahood that undergoes the change; for its essence, which is the Atman, is beyond all change. When it is said that the Jivas undergo the process of change in evolution, it must be remembered that only the factors that constitute Jivahood, or individuality, undergo change and not the basis of Jivahood, which is the Atman. Hence, for the Vedanta, there is the evolution of relative Jivas but not of ultimate realities. Even a miracle cannot destroy the ultimate essence of things.