RI Rationalism Descartes 2023

Sources of knowledgeRationalism: Descartes

2 Lecture Overview 1 Clear & Distinct ideas –further building blocks Strengths God and Cause & Effect 4 3 2 Cogito –the first building block Credit to : https://www.behance.net/diegocarbonell

Descartes•Another key figure of Rationalism, Founder of Modern Philosophy•Saw Reason as the way to counter Scepticism•Approach: discover infallible building blocks which cannot be doubted –this is the foundation•Then use the infallible ‘glue’ of deduction to derive other beliefs, especially of the external world

Cogito –the first building block•One key block: the Cogito•Properly Basic: not based on any prior belief and thus self-validating•“In the very act of doubting, my existence is revealed: even if I am deceived, I must exist in order to be deceived; even if I am dreaming, I must exist in order to dream. In fact, I can be certain of my existence only so long as I’m thinking. I can’t possibly conceive my non-existence here and now, for to conceive is to exist. However, if I ceased to think, I couldn’t assert my existence; I couldn’t know that I exist, though I possibly might exist even then. Finally, I know that I’m conscious because my consciousness is directly presented to me; it’s not represented to me by an idea. Descartes referred to such self-evident truths as simple intuitions–and he said that such particular truths lead us to more general truths (Tlumak, Classical Modern Philosophy, 23) I think therefore I am

But how to recover the rest of our knowledge?•Even if we were to accept the Cogito (setting aside Stroud’s objection), how do we recover our body of knowledge from just that one proposition?•Hard to see how the Cogito (or even TAs in general) can give us knowledge of the external world•E.g. I exist. And then? How to know that the external world exists? Think Evil Demon!

More Building Blocks•Upshot: Descartes has to find moreof such infallible, self-justifying beliefs•How? With the Cogito, Descartes believes he has found the key to find these other beliefs•Descartes: I know some things, for e.g. that I exist and that I am a thinking thing•If so, then I must already know how to identify infallible knowledge; I only need to make this means of identification explicit•Key: “everything which we conceive very clearly and very distinctly is wholly true”•Essentially, it is an idea that we cannot but accept as true.

The indubitability of Clear and Distinct Ideas•But why trust C&D ideas? •Because they are the results of mental intuition and leave no room for doubtBy ‘intuition’ I do not mean the fluctuating testimony of the senses or the deceptive judgement of the imagination as it botches things together, but the conception of a clear and attentive mind, which is so easy and distinct that there can be no room for doubt about what we are understanding. Alternatively, and this comes to the same thing, intuition is the indubitable conception of a clear and attentive mind which proceeds solely from the light of reason … Thus everyone can mentally intuit that he exists, that he is thinking, that a triangle is bounded by just three lines, and a sphere by a single surface Descartes, Rules for the Direction of the Mind; emphasis added

Examples of C&D ideas•Basic claims of logic: •Law of non-contradiction: it is impossible for both p and ~p to be true at the same time (I cannot be both intelligent and stupid at the same time)•Law of excluded middle: Either p or ~p must be true, i.e. a proposition is either true or false (either it is true that I am beautiful or it is false)•Law of identity: each thing is identical with itself (I am me)•Basic claims of arithmetic: 2+3=5•Basic claims of geometry: a triangle has 3 sides

•Analytic a priori propositions: where the predicate is contained within the subject•E.g. “A bachelor is an unmarried man”•As opposed to “Mr Lee is wearing a yellow shirt”•Importantly, these are all a prioripropositions, i.e. they can be known prior to experience Examples of C&D ideas

Moving beyond the foundation•With these basic building blocks, it appears that we can get more complicated a priori claims•Example: all of mathematics! Knowing the requisite axioms, we can arrive at proofs such as “the sum of two odd numbers is even”Even number = 2n, Odd number = 2n + 1, where n is whole number; Laws of arithmetic applyLet the odd numbers be a and bThen a = 2n+1b = 2m+1 for whole numbers n and ma+b= 2n+1+2m+1= 2m+2n+2= 2(m+n+1)= 2p where p is whole no.But this is of the form 2n and hence even (QED)