Rene Descartes is rightly called the father of modern philosophy. In him the modern tendency to free philosophy from the aesthetic interests of the ancient Greeks and the theological bent of the medieval scholastics, and to rest it mainly on scientific and rational foundations, took its origin. Descartes recognised that the principles of philosophy should be based on self-evident truths, which are certain for all time and free from doubt and dispute, even as the axioms of mathematics are, from which we can correctly deduce all other truths in a logical order, provided we do not go wrong in our calculation and reasoning. His problem was to find out such a self-evident principle on which to base all further discovery and research.
Descartes began with doubt. He found that we cannot trust sense-experience, for it often deceives us and it is hard to assure ourselves of the reality of things which appear to correspond to our sensations. We cannot even be sure of the reality of our own bodies; perhaps we are dreaming that we have bodies; perhaps we are dreaming that we are seeing objects outside. How can we know whether we are waking or dreaming? We may be entirely mistaken in believing what we see. Perhaps the world is only in the mind, in imagination. It may be just an illusion produced by thought. Everything may be doubtful, even mathematical truths. The only certainty seems to be that there is nothing certain!
Now comes the stroke of genius in Descartes. He discovered that though all things may be doubtful, the fact that we doubt is itself not doubtful. The basis of doubt cannot be doubted. There is doubt, thinking; this is certain. And so the existence of the doubter or the thinker, too, must be certain. 'Cogito, ergo sum' concluded Descartes. "I think, therefore, I am." From the fact of thinking it is to be concluded that the thinker is a spiritual being; I am, and I must be essentially spiritual in nature. This knowledge is the only certain one, and it does not come from sense-perception or imagination. Here is the self-evident rational basis for all deduction in philosophy. This is a universal and necessary proposition.
In the Vedanta we have a reversal of this process of deduction followed by Descartes. The former deduces the thought from the thinker and not the thinker from the thought. Instead of saying "I think, therefore I am", it would say "I am, therefore I think." The Self, to the Vedanta, is prior to the act of thinking. What is indubitable and self-evident is not the fact that we think, but that we are. The awareness of the existence of one's own self is not deduced from thinking or doubting. It is the only self-evident truth beyond all proofs, it being the source of all proofs. As the famous dictum of Shankara goes, "no one doubts his own Self", and this is not the result of a chain of reasoning or a deduction from a process of empirical functioning of thought. In short, to the Vedanta, the highest Consciousness is of the Self, and this Consciousness is identical with Existence. We cannot make a distinction between 'sat' and 'chit', Existence and its Consciousness. The experience of the world through the senses and the mind, the various processes of thinking and the different implications of this experience are all offshoots of the consciousness of the Self. Thought does not precede the thinker; the thinker precedes the thought and the consciousness of the thinker precedes the fact of his being a thinker.
Descartes makes his 'Cogito ergo sum' the starting point of his proof for the existence of God. 'I think, therefore, I am' is an undisputed truth. Thought must exist, for the thinker exists. Well; now, take the thought or the idea of God which arises in the mind. Naturally, as every effect has a cause, the idea of God must have a cause, a basis. It is also known that the cause cannot be less than the effect; if there is any value or reality in the effect, it must be present in the cause, also. For, nothing can come from nothing; this, too, is a self-evident truth. The effect cannot have, therefore, a greater reality than the cause. So the idea of God, which is of an infinite Being, cannot arise from me, a finite being. This idea of the infinite must therefore be due to the existence of an infinite cause thereof, which must have placed this idea in me. This infinite existence which is responsible for the rise of the idea of the infinite in me is God. Thus, the existence of God is proved.
Descartes could have as well argued this out better in the following manner: The idea of the infinite is in my mind; it has arisen from my mind. But I am a finite being; how, then, has this happened that a greater effect has arisen from a smaller cause? This cannot be, for the cause is always at least as great as the effect. But it is also true that the idea of the infinite has arisen in my mind, it does not come from some other's mind. And my idea is real, it exists, for I, who am its cause, exist as a reality,—my existence cannot be doubted, 'Cogito ergo sum'. Hence, if my idea of the infinite exists, and if it must have a cause, and if I am its cause, and also if the cause is not less than its effect, I must be an infinite being. Infinite Being must be God, for there cannot be two infinite beings. Thus, the proof for the existence of God would, at the same time, be proof of my identity with God. This reasoning, had he but followed it, would have taken Descartes nearer to the truth of the Advaita Vedanta, that the individual soul is essentially one with the Absolute. But this Descartes did not do; he left his self in its finite individual state. This self of Descartes, therefore, is different from the Atman of the Vedanta.
The argument is also justified by its moral aspect, which makes the infinite the goal of the moral urge within us, which ever makes us strive to reach it, to become perfect, and to discover the implication of its existence in the very feeling and acceptance of our being finite and imperfect. Descartes resorts to this aspect of the argument and says that a reference to the infinite and perfect being is necessarily included in the recognition of one's finitude and imperfection. I know that I am finite; therefore the infinite exists. The knowledge of limits points to what is beyond limits.
This conclusion of Descartes is quite acceptable to the Vedanta, for whom Mumukshutva, or the longing for liberation from finitude, which arises in the self, can have meaning only when the Infinite exists. But to it, the proof for the existence of the Infinite consists not in mere logical deduction, but in an inner persuasion and conviction independent of reasoning, an essentially moral urge, though the aspirant may later on, for his satisfaction and strength, seek to justify the validity of this inner call by resort to reasoning. What the Vedanta calls viveka, or the discrimination between the real and the unreal, which is the fundamental requisite of a spiritual aspirant, is a rational conviction of a higher order, in which the moral urge directing the aspirant to the Eternal is necessarily implied as an invariable concomitant.
Descartes comes to the conclusion, from the nature of the perfection that God is, that God is the ultimate causeless cause, by an argument akin to that of Aristotle. Only the admission of such a God can avoid an infinite regress in our search for an ultimate cause. Descartes holds that the innate idea of God that rises in the mind is sufficient proof of God's having made man in His own image. God's existence is the precondition of the existence of all other things, including the individual souls, and also of His idea in the human mind. There cannot be an idea of God without the existence of God. God is incorporeal, intelligence, all-knowing, good and just. He is omnipotent, eternal. He has no changes, no modes of attribute, no modifications. As a deeply religious man, Descartes regards reason as valid only when it does not conflict with authority. This is the position of the Vedanta, too, for which unaided reason is more a hindrance to success in spiritual pursuits than a safe guide. The value of reason rests on its conforming to sruti, or intuitional revelation.
The existence of physical things which are extended in space outside, Descartes proves by appeal to our sensations which, according to him, ought to be caused by the presence of these things. Things or bodies are substances, and their existence is extra-mental, they are not dependent on our thoughts. Thus, Descartes posits three existences or substances: God, mind and physical things or bodies. The mind and the physical bodies are different from each other, known only through their functions and properties; but both these are dependent on the supreme substance, God. Bodies are moved by God, for they have no capacity for independent motion; they are passive, inert. And their motion obeys the laws of mechanics. But Descartes does not think that God can interfere with the mechanistic scheme of the world. God, when He created the world, endowed it with a certain amount of motion and rest, and He confines Himself to the operation of matter within the limit prescribed by Himself originally. There cannot be increase in the amount of motion, though God could have made the world otherwise, if He liked, at the time of creation. Motion and rest, which are properties of matter, do not increase or decrease.
Mind, according to Descartes, is without the extension characteristic of bodies. It is absolutely different from bodies. The mind and the bodies are not dependent on each other, though both are dependent on God. There is a dualism between the mind and the bodies, and the latter are determined by the laws of mechanics. The mind is not a part of the physical world which consists of extended bodies. Descartes has no teleology about matter and its laws. No purpose or final cause determines the ways of the world. The mechanism of physical science reigns supreme in the world of matter. Even the human body, though organic in nature, is mechanical in its functions, and is moved by the heat generated in the heart. The body works not purposively but automatically like a machine.
The most curious part of the philosophy of Descartes is his view that the mind and the body do not interact in order to produce changes, and that their apparently mutual interaction is really the agreement between their functions due to their running parallel to each other like two well-adjusted clocks which show the same time, though they do not influence each other in any way. Descartes is not inclined to admit any dependence of body on mind or vice versa. The parallelism in the workings of the mind and body is attributed to the will of God, Who has made them in that way.
There is a radical difference between Descartes and the Vedanta in regard to the relations subsisting among God, world and soul. Descartes confuses between the mind and the soul and he seems to think that the mind is the soul or the inner self of a person. To the Vedanta, the soul is consciousness. The Supreme Soul, or God, is the absolute consciousness existing as the background of the activities of the mind. The individual soul, however, is the very same consciousness manifest through the medium of the mind and thus partaking of the temporal and fluctuating characteristics of the mind. The mind as such is inert, has no consciousness in it; it is merely a vehicle of individuality, and its consciousness is borrowed from the supreme Soul. The mind, therefore, cannot be the soul.
God is not cut off from the world and the souls; it is God that appears as the world and the souls. If God, as Descartes thinks, is different from the world and the souls, there can be no relation between Him and these, so that He cannot even set them to work parallelly and independently. By holding that God is other than the mind, Descartes would be stultifying his own position that God has impressed His idea on the mind of man. Consequently it would also follow from the dualism between God and man that man cannot have knowledge of God, cannot have even any kind of relations with Him. Sometimes Descartes finds himself forced to establish a causal relation between God and the world of individuals, in order to answer to the objection that no interaction would be possible between them if strict dualism or pluralism of substances is admitted. Descartes does not remove the discrepancy given rise to by his contradictory views that God is the only real substance and also that God, world and mind are three real substances. He creates great gulfs without trying to bridge them.
The theory of parallelism propounded by Descartes is opposed to facts of experience. The feelings and passions experienced by individuals prove the interaction between the mind and the body. The complex emotions that arise in the mind and the different sensations of hunger, pain, colour, sound, etc., cannot be exclusively the functions of the mind alone or the body alone; these are results of a mutual interaction between the mind and the body. According to the Vedanta, man is neither pure Spirit alone, nor pure mind alone, nor pure body alone. Man is a blend, together, of spirit, mind and body. The spiritual Self, the mind and the senses together constitute an individual. We are an organic whole, not merely divided parts, as Descartes thinks. The highest organism, however, is Ishvara, in Whom the world and the individuals are merged to form a wholeness of being. Ishvara's will is the supreme mover, director and organiser of all things. To the Vedanta, the world and the individuals are not realities independent of Ishvara, but appearances of Ishvara Himself. Ishvara is the only reality, Brahman viewed from the empirical standpoint. The individual, that is man, is a part of Ishvara, Who is the Inner Controller of all beings, and in essence man is inseparable from Ishvara. This identity is realised when the independent and distorted functioning of the will of man ceases and he allows his higher intelligence to rise to the infinite that is Ishvara. Ishvara's relation to the world and the individuals is something like the relation that the waking individual has to the dream world and to the individuals seen in dream. The differences among God, world and the individuals are therefore mere makeshifts of the empirical consciousness, while in truth there is only one Being which is called God in relation to the empirical world and the individuals, and the Absolute, in itself. The trinity of substances in Descartes militates against reason and fails to accord with experience.
Descartes raises a point which is not in disagreement with the Vedanta when he says that God does not interfere with the workings of the world which He Himself has determined when creating the world. In the Vedanta, Ishvara does not so much create the world as make possible the manifestation of the unmanifested potencies of the unliberated individuals which lay dormant at the time of the dissolution of the world during the previous cycle. All that happens in this world is in perfect accordance with the will of Ishvara and hence the view that He does not change the present scheme of the world into something else is no denying of His omnipotence. He is all-powerful. He can make the world other than what it is; only there is no need for His doing so. There is no reason why He should interfere with the movements of the world when he Himself has willed them to be such.
But the explanation of the world by the laws of mechanics offered by Descartes is in no way tenable according to the Vedanta. The world appears to work in strict obedience to the laws of mechanics, because our ways of looking at it are limited to the operation of the space-time phenomenon, which makes us feel that causation is a straight-line process of the temporal precedence of the cause in the production of effects. But the truth is otherwise. The world of matter is not segregated from man or God. An organic unity cannot be explained by mechanical laws even as the functions of the human body cannot be subjected entirely to the mathematical laws of physics. A higher vision and understanding disclose the fact that there is a supreme end towards which the apparently mechanical operations of matter tend, that the movements of the world are purposive, and that the fulfilment of the phenomena of the world and the individuals is in the final realisation of the Absolute. Mechanics is what is seen from a surface-view; as its implication hidden behind sense-perception is the great truth that all change and motion is a yearning to unfold within oneself the reality that is immutable.