The Library of Original Sources, Vol 6


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The Beginning of Modern Philosophy

We saw in the second volume of this series that Greek philosophy had a consecutive development starting with Thales and reaching its climax in Aristotle. Modern philosophy, beginning with Descartes, forms another connected story of the evolution of thought. The Greek philosophers attacked mainly the problem of what is the permanent reality in the universe: modern philosophy has begun to see that the problem of the true nature of the universe is bound up with the question of the real nature of the self.

Descartes (1596–1650) tried to sweep away all uncertainties and start from one absolutely certain fact, "Cogito, ergo sum," as he expressed it,—"I think, and in so thinking I exist." Only what appealed to his mind as clearly as this prime truth was to be accepted as a fact. He believed in the existence of God because he thought there must exist some perfect, infinite Being which is the source of imperfect, finite man. He felt that he could trust his senses as to the material world because such a Being would not deceive. Therefore he accepted the existence of matter as a substance co-ordinate with mind, the essence of mind being thought, the essence of matter being extension, the source of both being God.

Out of this conception of the duality of the universe, rose the question of how mind and matter can act on each other. Geulincx (1625–1669) denied the possibility of any interaction. He thought mind and matter to be like two clocks that run in harmony, not because they interact, but because both are controlled by their maker. Thus Malebranche (1638–1715) declared that "we see allthings in God," that "our minds exist in God as matter exists in space," that things are known to us only through ideas, and these ideas come from God.

Spinoza (1632–1677) transformed the dualism of Descartes into a monism by making God the sole true substance, and mind and matter only His manifestations. Leibnitz (1646–1716) sought to overcome Descartes’ dualism by supposing the universe to be, not one great unity, but made up of an infinite number of individualities, or, as he called them, monads. He makes the essence of substance to be life, mind, and activity. Each monad is an individuality, but some only move, others live, others think though unconsciously, the highest are self-conscious. God is the supreme monad whence all others radiate as light from the sun. The harmony of the world was established at its creation. Thus Leibnitz practically added the conception of life and mind to the atomic theory of the Greek Demokritos.

Locke (1632–1674) took up the examination of the contents of the mind anew. He opposed Descartes’ doctrine of innate ideas and Leibnitz’s belief in the possibility of unconscious thought. He thought the soul to be at the beginning a tabula rosa, an "unmarked tablet," and that all ideas come from experience. His analysis of the ideas of the mind marks the beginning of psychology. He agreed with Descartes in our certainty of our own existence, argued for the existence of God as the cause of our existence, and believed in the existence of things or matter as the cause or occasion of our ideas. Where he got his principle of causality he does not explain.

This idea of Locke’s that substance is an abstract idea presupposed as the cause of our sensations is the starting ground of Berkeley’s idealism. Let us take an illustration. What can we actually mean by a thing—for instance, a bell? We have a sensation of sound, another of sight, a feeling of hardness or resistance, a temperature sensation of coldness, perhaps a bitter taste of the brass. All these sensations are states of our own consciousness, but they are continually recurring together, and we take for granted something that we call a bell as their cause. Yet all we really experience is a cluster of sensations. Now Berkeley admits that we do have such clusters of ideas, and that consequently our experience is exactly the same under his system as under the most out and out materialism. Where Berkeley differs from materialism is in his answer to the question, "What is the real nature of that somethingwhich we presuppose as the cause of these groups of sensations?" Berkeley’s argument, in brief, is this: All we can actually experience is our self and the states of our own consciousness—all mental; the only self-acting cause we know is our own will—also mental; since, then, the only reality and the only cause we can actually know are mental, what right have we to suppose this unknown something to be anything but mental? Thus Berkeley argues dead matter out of existence and in its stead puts God, the cause of all our sensations. Nature is a symbolism through which God speaks to us.

Hume (1771–1776) hurled philosophy from idealism into scepticism. Starting from Locke’s theory that all knowledge comes from experience, he argued against the possibility of any sure knowledge or science whatever. He declared that he could not find the self at all, that he saw no necessary connection between ideas, that cause and effect are simply habits of thought formed by custom, and that therefore any certain knowledge is impossible.

This scepticism of Hume woke Kant (1724–1804) "out of his dogmatic slumber," and incited him to examine the elements of the mind. His problem was, "How is mathematics possible? How is natural science possible? Is metaphysics possible?" He found elements in the mind besides those that come from experience. He showed that although the contents of our minds are given by experience, the form is furnished by the active mind itself. Space and time, cause and effect, design, reciprocity are all forms of thought given by the active mind to phenomena, and the possibility of any consciousness whatever depends upon the unifying activity of the self. Things in themselves we cannot experience, phenomena must come under the laws of thought in order to be correlated with the rest of our consciousness. This is Kant’s answer to the problem of the possibility of knowledge. The laws of thought hold good for all experience, but cannot go beyond it. Nature in itself we cannot experience, but only its manifestations as the phenomena of our consciousness. The soul is a thing in itself; we can never grasp it. But for the very reason that it is not a part of our experience, the soul in itself may not be bound by the laws of experience and the will may be free. This is the necessary basis of morality. So, too, God may exist outside the field of experience, and faith is always possible.

The above outline is best amplified in the words of the thinkers themselves. The development of philosophy since Kant belongs to a later volume.


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Chicago: "The Beginning of Modern Philosophy," The Library of Original Sources, Vol 6 in The Library of Original Sources, ed. Oliver J. Thatcher (Milwaukee, Wisconsin: University Research Extension Co., 1907), 39–41. Original Sources, accessed July 23, 2024,

MLA: . "The Beginning of Modern Philosophy." The Library of Original Sources, Vol 6, in The Library of Original Sources, edited by Oliver J. Thatcher, Milwaukee, Wisconsin, University Research Extension Co., 1907, pp. 39–41. Original Sources. 23 Jul. 2024.

Harvard: , 'The Beginning of Modern Philosophy' in The Library of Original Sources, Vol 6. cited in 1907, The Library of Original Sources, ed. , University Research Extension Co., Milwaukee, Wisconsin, pp.39–41. Original Sources, retrieved 23 July 2024, from