Descartes and Skepticism

1. Descartes and Skepticism No Beliefs Left Standing…

2. Propositional Knowledge • Knowledge can be many things: • Acquaintance knowledge: direct knowledge of some person. • Practical knowledge: is knowledge how to do things. • Propositional knowledge, or knowledge that some proposition is true. • Propositional knowledge is the most basic kind of knowledge.

3. Definition of Knowledge • Knowledge is: • Justified: is believed because of the belief forming processes, reasons, etc • True: corresponds to reality • Belief: a mental state wherein the agents holds a proposition to be true • To see this is the proper definition, just subtract one of these.

4. Descartes on his Method • Descartes says that, from an early age, he had accepted many false opinions as true. • And so, his opinions were doubtful and uncertain. • I had to undertake seriously once in my life to rid myself of all the opinions I had adopted up to then and to begin a fresh from the foundations, if I wished to undertake something firm and constant in the sciences. • So, Descartes says, to do this, he has waited until he was mature to do so. • When, he says, he has leisure and solitude.

5. Method Again • Descartes says he need not prove his opinions to be false. • Still, he says, he must reject his beliefs. • I must avoid believing things which are not entirely certain and indubitable, no less carefully than those things which seem manifestly false. The slightest ground for doubts that I find it any will suffice for me to reject all of them • Descartes says that there is no need to investigate all his beliefs individually. • Instead, he says, he will undermine their sources.

6. The Senses- Level 1 • Descartes notes how much of his knowledge, as such, has come through his senses. • But these have deceived him. • And, as he says, it is prudent never to trust that which has deceived us, even once. • Does he know anything that has come from his senses?

7. Particular Sensory Items? • Still, Descartes says, there is knowledge- particular things- from his senses that he cannot doubt. • And these particular things, he says, are simple, such as the fact that he is writing, with his hands, has a body, etc. • Either he is insane, or he knows these things. • Yet does he?

8. Dreaming- Level 2 • Yet as Descartes says, if he were dreaming, his particular sensory beliefs would be false. • And so, they would not be knowledge. • …I recall having often being deceived in sleep by similar illusions and, reflecting on this circumstance…I see clearly that there are no conclusive signs by which one can distinguish clearly between being awake and being asleep, • Descartes cannot tell if he is not dreaming, at any given time. • And so, his particular beliefs are not knowledge.

9. Dreaming Again • Still, Descartes says, particulars sensory belief must have some sources. • And so, they are like pictures and painting. • So, at least there must be real writing and hands somewhere for him to have these ideas of colors, etc. • Yet as Descartes says, we might just mix and match colors,, etc., and make thing up! • So again, such true elements of other ideas are not knowledge.

10. Math- Level 3 • As Descartes says, physics, astronomy, medicine, etc., deal with composites, and so are all uncertain. • But math and geometry, he says, deal with only simple and general things. • Still, Descartes says • …there is an omnipotent God who made me. How do I know that he has not brought it about that there is no earth, sky, no extended thing, no shape, size, etc, all the while insuring that all these things appear to me just as they do now? • Yet how is this argument different from the dreaming argument? • Descartes says that, when he uses math or geometry, this being could make him go wrong. • Therefore, even math is not knowledge.

11. Accident Prone • Descartes says that that even if God is not doing this, we might be imperfect. • So we might make even more mistakes. • I will consider myself as not having hands, or eyes, or flesh, but as falsely believing that I have all these. I shall stubbornly and firmly persist in my meditation. Even if it is in not in my power to know any truth, I shall do what is in my power. • As Descartes says, we may not know anything. • Skepticism may be inevitable.

12. The Skeptical Argument • Although Descartes does does not say so exactly, his general argument is: • I know x only if I can satisfy condition y. • Yet, I cannot satisfy condition y. • Therefore, I do not know x, either. • And so, Descartes concludes, he really does not know anything.

13. Laziness • Descartes reminds himself that he has spent a lifetime acquiring unjustified beliefs. • So, he will end up believing things, again. • I must make an effort to remember that my habitual habits keep coming back. Despite my wishes, they capture my belief, which is as it were bound over to them as a result of long occupation and law of custom. • To counter his natural laziness, Descartes says that he will not consider his beliefs probable. • Instead, he will consider them false.