Principles of Philosophy
The Philosophical Writings of Descartes
Brackets] enclose editorial explanations. Small ·dots· enclose material that has been added, but can be read as though it were part of the original text. Occasional •bullets, and also indenting of passages that are not quotations, are meant as aids to grasping the structure of a sentence or a thought. The basis from which this text was constructed was the translation by John Cottingham (Cambridge University Press), which is strongly recommended. Each four-point ellipsis . . . . indicates the
... . indicates the omission of a short passage that seemed to be more trouble than it is worth. Longer omissions are reported between square brackets in normal-sized type.-Descartes wrote this work in Latin. A French translation appeared during his life-time, and he evidently saw and approved some of its departures from or additions to the Latin. A few of these will be incorporated, usually without sign-posting, in the present version.-When a section starts with a hook to something already said, it's a hook to •the thought at the end of the preceding section, not to •its own heading. In the definitive Adam and Tannery edition of Descartes's works, and presumably also in the first printing of the Principles, those items were not headings but marginal summaries. Contents Part 1: The principles of human knowledge 1 Part 2: The principles of material things 22 Part 3: The visible universe 42 Part 4: The earth 58 Principles of Philosophy René Descartes 1: Human knowledge Part 1: The principles of human knowledge 1. The seeker after truth must once in his lifetime doubt everything that he can doubt. We're bound to have many preconceived opinions that keep us from knowledge of the truth, because in our infancy, before we had the full use of our reason, we made all sorts of judgments about things presented to our senses. The only way to free ourselves from these opinions, it seems, is just once in our lives to take the trouble to doubt everything in which we find even the tiniest suspicion of uncertainty. [Here and throughout this work, 'preconceived opinion'-following Cottingham's translation-translates praejudicatum. Sometimes, for a change, it will be translated as 'prejudice', but always meaning something believed in advance, believed long ago and then hung onto. It lacks much of the force of 'prejudice' as we use that word today.] 2. What is doubtful should even be considered as false. It will be useful ·to go even further than that·: when we doubt something we should think of it as outright false, because this will bring more thoroughly into the open truths that are certainly true and easy to know. But this doubt shouldn't be carried over into everyday life. While this doubt continues, it should be kept in check and used only in thinking about the truth. In ordinary practical affairs we often have to act on the basis of what is merely probable, not having time to hold off until we could free ourselves from our doubts. Sometimes we may-·for practical reasons·-even have to choose between two alternatives without finding either of them to be more probable than the other. The reasons for doubt regarding sense-perceptible things. When we're focussed on the search for truth, we'll begin by doubting the existence of the objects of sense-perception and imagination. There are two reasons for this. (1) We have occasionally found our senses to be in error, and it's not wise to place much trust in anyone or anything that has deceived us even once. (2) In our sleep we regularly seem to see or imagine things that don't exist anywhere; and while we are doubting there seem to be no absolutely reliable criteria to distinguish being asleep from being awake. The reasons for doubting even mathematical demonstra- tions. We'll also doubt other things that we used to regard as perfectly certain-even rigorous mathematical proofs, even principles that we used to regard as self-evident. ·There are two reasons for this too·. (1) We have sometimes seen other people make mistakes in such matters, accepting as utterly certain and self-evident propositions that seemed false to us. (2) More important: we have been told that we were created by a God who can do anything. Well, for all we know he may have wanted to make us beings of such a kind that we are always wrong in our beliefs, even ones that seem to us supremely evident. ·This may seem extravagant, but it shouldn't be brushed aside·. We have encountered some cases of error about something of which the person was perfectly certain, and it's equally possible that certainty is always accompanied by error. 'Mightn't we have been brought into existence not by a supremely powerful God but by ourselves or by some other creator?' Yes, but the less powerful our creator is, the more likely it is that we're an imperfect product that is deceived all the time! Principles of Philosophy René Descartes 1: Human knowledge 6. We have free will, enabling us to avoid error by refusing to assent to anything doubtful. Still, whoever created us and however powerful and however deceitful he may be, we experience within ourselves a freedom to hold off from believing things that aren't completely certain and thoroughly examined. So we can guard ourselves against ever going wrong. We can't doubt that we exist while we are doubting; and this is the first thing we come to know when we philosophize in an orderly way. In rejecting everything that we can in any way doubt, even pretending to think it false, we can easily suppose that there's no God and no heaven, that there are no bodies-so that we don't have bodies, hands and feet and so on. But we can't suppose that we, who are having such thoughts, are nothing! 'At a time when I am thinking, I don't exist'-that's self-contradictory. So this item of knowledge-I'm thinking, so I exist-is the first and most certain thing to occur to anyone who philosophizes in an orderly way. 8. In this way we discover how soul and body differ, i.e. what the difference is between a thinking thing and a corporeal one.