From the Sankhya to the Vedanta; this substance of the great systems of Hindu Philosophy is enough to show that, even as Vedanta tells us, they are but parts of a magnificent whole, and deal with the many problems of life from different points of view. We begin with certain assumptions, and then, bring a gradual process of thought, criticise, correct, or confirm them.
For instance, we begin with the idea that Prakrti or Nature is the supreme creator of life, and there is no place for God in the scheme of things; that the soul is altogether different from all that is in the world or the body in which it abides; that there is no joy in life, and pleasure itself is but a form of pain; that all desire is essentially evil; that there is an inherent opposition between knowledge and action; and that we can attain to freedom from the bondage of life only by means of a total renunciation of action and withdrawal from the world.
Then, slowly and gradually, we understand the implications of the ideas of Nature and God, the real character of the soul and its relation to the body and the world, the nature of knowledge and action, good and evil, pleasure and pain, desire and its result, and come to the conclusion that there is no inherent opposition between the idea of Nature and of God, and that if we believe, as we must, that the working of the great forces of Nature is characterized by both goodness and intelligence, we transform the idea of Nature itself into that of God.
That the soul, though different from many things in the world, cannot be dissociated from them, nor can its idea be separated from that of the intellect, which is said to be an expression of Nature itself; that there is joy in each true act of creation, and it is this joy that sustains the world; that the motive of each action is positive, the attainment of some satisfaction, pleasure, or good, besides the avoidance of their opposites; that there is an element of goodness in each desire, so far at least as the person who possesses it is concerned, and it can be in conformity with Dharma too; that the difference between pleasure and pain, and good and evil is one of degree, not kind; that there is no essential opposition between knowledge and action, and there can be no action without knowledge and no knowledge without action; and that freedom from the bondage of life is attained by living in the world, doing heroic deeds without injury to any one, attaining the highest that is in it, understanding the true nature of the soul and all that is called life, and living in a state of equilibrium in the midst of all actions and the experience of pleasure and pain. The whole process is rational or intellectual, and is illuminated by a wealth of ideas and imagery, and embodied in a form which, when we understand it, is as clear as it is coherent and concise, and is without a parallel in the history of human thought. At the same time there is an attempt to transcend the limitations of human reason too, and we are led into the realms of the Unknowable, the city of the god of Death, as well as the kingdom of eternal life and light, the abode of the Supreme. Thus, physical science and logic and ethics, the laws of life and the theories of knowledge and action together with psychology and metaphysics, the origin and essence of things, the nature of the soul, and the idea of God are all integrated together to make a great whole which, when perceived from different points of view, gives us a number of Darsanas or clear visions of life, and constitutes the end of all our quest of Truth.
Indeed, it is no exaggeration to say that to understand these systems of philosophy is to understand the foundations of ancient thought and the essence of what is described in the sacred books. They all claim to derive their origin from the Vedas and the Upanishads; and the Mimansa tells us that the subject-matter of the Vedas is nothing less than the laws of Nature and the life of man, or Dharma that sustains the universe. It also explains the method by means of which we can understand them in this light.
The Upanishads are said to be an exposition of the secret doctrine of the Vedas, and we can now understand that they are really so. A great deal of what they contain is pure thought; and the same ideas have been expressed in the Vedas in a different form. But a considerable portion of the Upanishads too has been composed in symbolic form, and would need to be interpreted in the same manner as the Vedas, and in accordance with the method described in the Mimansa. The great Epic of the Ramayana is said to be a Veda; while the Mahabharata, the greatest of all, has been described as the fifth and last of the Vedas; and we are told that what "is in it is elsewhere too; and what does not occur in it, occurs nowhere else;" for it includes the entire range of human thought from Sankhya to Vedanta, when interpreted in accordance with the method explained in the Mimansa. The same is true of the Puranas too; and it is for this reason that the Mahabharata is spoken of as "itihasa or history of the Puranas"; but we need to understand them also in the same manner.
From science to philosophy: An examination of the different systems of philosophy will show that the whole process is purely rational or scientific; and the ancients must have known a great deal of physical sciences, in a strictly modern sense of the term, to be able to describe them in this form. Their conception of the "elements" was indeed different from our own, for they conceived of them as great elemental forms and forces of Nature, Earth, Water, Fire, Air, and Ether out of which all material objects are formed. The Mimansa tells us that the Vedas deal with the great laws of Nature and their bearing on the life of man; and what great truths a proper study of their text will disclose would be difficult to say. But the Sankhya tells us that all matter is formed out of the mind; and the Nyaya and the Vaiseshika discuss the nature of the atom, refer to its division, and tell us how, though invisible, it can yet be perceived. They also define Ether and sound, describe the character of mass and action, and examine the properties of the "elements". The Mimansa deals with the conception of Time as something purely intellectual, speaks of its connection with action, and tells us how it can be described. It also gives us a scientific division of animals into vertebrate and invertebrate, and refers to Jyotishtoma or the rays of light. There is also a reference to the many great things that can be achieved by means of Yoga; but if we understand the text correctly, we find that the principal idea is purely scientific, for we are told that a body can be made to become light as cotton by means of its adjustment to motion; and we can hear wonderful sounds by concentrating on the essential character of sound.
Indeed, the great attempt of the ancients was not only to understand the laws of Nature, but also to integrate them into the life of man; and when they conceived of man as a microcosm, they fused science into psychology, and conceived of the six systems of philosophy; the Sankhya based on a broad survey of Nature, and the rest on the five faculties of man, his senses, mind, ahankara, intellect, and the soul. Thus they transformed science into philosophy through the medium of psychology.
From philosophy to religion: The same process of thought enabled them to transform philosophy into religion; for we find that it is these systems of philosophy which constitute the bases of the different systems of Hindu religion, and exhibit the same unity of thought as the systems of philosophy themselves. It is sometimes believed that philosophy and religion are two different things, the one based on reason, and the other on faith and the two have little in common with each other. While this is true of some great systems of religion, like Christianity and Islam, the essential idea of what are called the Hindu systems of religion is purely philosophical, even as the basis of their philosophy is a knowledge of the laws of Nature and their application to the life of man. Indeed, the ancients conceived of religion as the highest art of life, an attempt to live in the light of the highest Truth as we understand it. Dharma, the term commonly used for religion was, accordingly, conceived to be action performed as a sacrifice, even as the Mimansa tells us; and that means nothing but good, intelligent, and joyous action, meant for the benefit of all; and it is this that sustains all life, both of the individual and the world, even as the word literally signifies. Religion is thus but a realization of the highest Truth, an experience of an ideal conception of life, necessitating a harmony of both knowledge and action, reason and emotion when the head and the heart act in unison, and meet in the awakening of the soul and the presence of God, the eternal principle of Goodness, Intelligence, and Joy (Sat-chit-ananda) that fills the universe.
The ancients believed that, as the ultimate object of all action is perfection, all life ministers to this end: and so all the fine arts, architecture, sculpture, painting, music and poetry the most magnificent temples, the finest carving and statues, the most delicate painting and effects of light and shade, the deepest notes of music, and the most beautiful poetry were pressed into the service of this idea of Dharma or religion. It has, indeed, drifted far away from its original conception; but its basic ideas still remain, and it is yet possible to trace them to their source.