I can't say I understood 100% of this book: it's not an introductory book and it needs some fundamental concepts to be known. After introduction and a short biography, three chapters are about three of most important books of René Descartes: [b:Discourse on Method|159418|Discourse on Method|René Descartes|https://d.gr-assets.com/books/1405624619s/159418.jpg|17612730], [b:Meditations on First Philosophy|30658|Meditations on First Philosophy|René Descartes|https://d.gr-assets.com/books/1405624521s/30658.jpg|6299110] and [b:Principles of Philosophy|1165783|Elementary Principles of Philosophy (New World Paperbacks)|Georges Politzer|https://d.gr-assets.com/books/1238027316s/1165783.jpg|1153468]. Each chapter consists of a summary of the book and then the author's explanation. The last chapter is some Q&A about Descartes' philosophy and also its relation and impression on philosophers who came after him.
The first thing about René Descartes philosophy is that he's a skeptic and rationalist who doubts about everything and the existence of himself first. He rejects any ideas that can be doubted, and then reestablishes them in order to acquire a firm foundation for genuine knowledge.
Perhaps one of his most famous quotes which I think everybody heard of it, is: Cogito ergo sum
or I think therefore I am
. What we might learn from this sentence by a deductive reasoning is:
1. I think;
2. Whoever who thinks, exists;
3. so I exist.
The problem here is the word "therefore" which leads us to this conclusion, which is not a rational reasoning: for proving that one exists one considers an "I" which exists first! What truly René Descartes means by this sentence is in fact: I think; I exist; my thinking depends on my existence.
Although he is a skeptic, surprisingly he doesn't doubt about existence of God! He prefers to not to have any doubt and just prove it (remember: he lives in the century of Galileo Galilei!). And in proving, he says: I can imagine a perfect God, the concept of perfection needs existence, if something doesn't exist we cannot call it "perfect"—so God exists!
Doesn't it sound like just playing with words and how can we imagine a perfect God in our limited minds?!!