De omnibus dubitandum, taught Descartes - doubt all things. Easily said - but how to do it? Try, for example to doubt that the laws of nature are always binding: one day a case may occur where nature makes an exception for some stone, and exempts it from the law of gravity. But how to find this stone, if one has the courage to admit such a possibility, even if one knew definitely that such a stone existed? p. 215

If there is something more in a living being than a pure mechanism, Descartes is bound in advance to miss it.

If there is a single initial error at the root of all the difficulties philosophy is involved in, it can only be the one Descartes committed when he decreed, a priori, that the method of one of the sciences of reality was valid for the whole of reality.

To accept the Church's monopoly of the subjective life, or to surrender it to muddled magic and vulgar superstition, was to set limits to the examination of human experience and the pursuit of truth. The inner life could not remain forever a no-man's land, where saints, gypsies, lords, beggars, artists, and lunatics had established squatters' rights and wasted precious human energy erecting an endless series of crazy, flimsy structures. In turning his back on the realities of subjective life, Descartes rejected the possibility of creating a unified world picture that would do justice to every aspect of human experience-that indispensable pre-condition for the 'next development of man.

Where is truth, where is reality? Over there at Grichkino, or here on this plain? Grichkino had ceased to exist for ever; must one then doubt the reality of its existence? And with it the reality of the existence of all the old world? Doubt everything? De omnibus dubitandum? But did great Descartes really doubt everything? No, Hume was right: the man who has once doubted all things will never overcome his doubts, he will leave for ever the world common to us all and take refuge in his own particular world. De omnibus dubitandum is useless; it is worse than storm and snow, worse than the fact that Nikita is freezing and that the bay is shivering in the icy wind. p. 131-132

Starting with "I think," Descartes fixed his attention only on the "think," completely neglecting the "I." Now, this I is essential. For Man, and consequently the Philosopher, is not only Consciousness, but also—and above all—Self-Consciousness. Man is not only a being that thinks—i.e., reveals Being by Logos, by Speech formed of words that have a meaning. He reveals in addition—also by Speech—the being that reveals Being, the being that he himself is, the revealing being that he opposes to the revealed being by giving it the name Ich or Selbst, I or Self.

When "the light of truth" appeared to Descartes, he immediately imprisoned his discovery within a logical formula: "Cogito, ergo sum." And the great truth perished, it gave nothing either to Descartes or to any one else. Yet it was he himself who taught: "De omnibus dubitandum." But then he ought first of all to have questioned the legitimacy of the pretensions of syllogistical formulae, which claim to be the only, invariable, expert appraisers of truth and error. Directly Descartes began to make deductions he forgot what he had seen. He forgot the cogito, he forgot the sum, in order to be sure of the ergo which has the power to constrain men's minds. p. 110

Descartes’ dictum: ‘There is nothing so absurd or incredible that it has not been asserted by one philosopher or another.

Descartes... his type of determinism is only partial. I call it disconnected... that the physical world and... our bodies, but not our minds operate mechanically... We're robots, but the mind is different... that "The will is by its nature so free that it can never be constrained." This is normally called Descartes' dualism... mind, soul or spirit, and matter... [M]atter operates according to one set of laws, and mind or spirit... to another.

Descartes' dualism... is explicitly contradicted by our theorem.

Descartes may have made a lot of mistakes, but he was right about this: you cannot doubt the existence of your own consciousness. That's the first feature of consciousness, it's real and irreducible. You cannot get rid of it by showing that it's an illusion in a way that you can with other standard illusions.

The irony is that in shifting the focus onto the individual human mind, which everyone agrees can be a pretty flimsy and wayward organ, Descartes had arrived at the closest thing to a certain basis for knowledge. If my own thoughts are the only indubitable ground I can stand on, apparently they aren’t so flimsy after all, at least not all the time. As an earlier follower of Descartes put it, “doubt is the beginning of an undoubtable philosophy.” Therefore the mind and its “good sense”—that is to say, human reason—are the only basis for judging whether a thing is true. With the “cogito,” as philosophers abbreviate it, and with the theory of knowledge that arises from it, which Descartes outlined in the Discourse on the Method and later works, human reason supplanted received wisdom. Once Descartes had established the base, he and others could rebuild the edifice of knowledge. But it would be different from what it had been. Everything would be different.

Modern philosophy is usually considered to have begun with Descartes (1596-1650), who lived a generation after Galileo. The following is the usual image of Descartes and his philosophy: During the Middle Ages philosophy stood - if it stood independently at all - under the exclusive domination of theology and gradually degenerated into a mere analysis of concepts and elucidations of traditional opinion and propositions. It petrified into an academic knowledge which no longer concerned man and was unable to illuminate reality as a whole. Then Descartes appeared and liberated philosophy from this position. He began by doubting everything, but this doubt finally did run into something which could no longer be doubted, for, inasmuch as the skeptic doubts, he cannot doubt that he, the skeptic, is present and must be present in order to doubt at all. As I doubt I must admit that "I am." The "I," accordingly, is the indubitable. As a doubter, Descartes forced men into doubt in this way; he led them to think of themselves, as their "I." Thus the "I," human subjectivity, came to be declared the center of thought. From here originated the I-viewpoint of modern times and its subjectivism. p. 98-99

When mons. Descartes's philosophical Romance, by the Elegance of its Style and the plausible Accounts of natural Phænomena, had overthrown the Aristotelian Physics, the World received but little Advantage by the Change: For instead of a few Pedants, who, most of them, being conscious of their Ignorance, concealed it with hard Words and pompous Terms; a new Set of Philosophers started up, whose lazy Disposition easily fell in with a Philosophy, that required no Mathematicks to understand it, and who taking a few Principles for granted, without examining their Reality or Consistence with each other, fancied they could solve all Appearances mechanically by Matter and Motion; and, in their smattering Way, pretended to demonstrate such things, as perhaps Cartesius himself never believed ; his Philosophy (if he bad been in earnest) being unable to stand the test of the Geometry which he was Master of.