Ethics
Baruch Spinoza
 The first part of the book addresses the relationship between God and the natural world. According to a traditional view, God exists outside of the universe, created it for a reason, and could have created a different universe if he so chose. Spinoza's picture is different. God is the natural world. Men and other natural things are his modes – a term usually understood to mean properties. Everything that happens follows from the nature of God, just as it follows from the nature of a triangle that its angles are equal to two right angles. Since God could not have had a different nature, everything that happens could not have been avoided. God didn't create the world for any particular purpose. The second part focuses on the human mind and body, and implicitly attacks several Cartesian positions: first, that the mind and body are distinct substances, each capable of existing without the other, but which can elicit changes in one another; second, that we know our minds better than we know our bodies; third, that our senses may be trusted, since our benevolent Maker made us incapable of disbelieving them; and finally, that despite being created by God we can make mistakes, namely, when we affirm, of our own free will, an idea that is not clear and distinct. Spinoza denies each of the aforementioned claims. The mind and the body are one and the same thing; "mind" and "body" are two ways of understanding the same thing. The whole of nature can be fully described in terms of thoughts or in terms of bodies. However, we cannot mix these two ways of describing things, as Descartes does, and say that thoughts cause actions in the body, or that changes in the body cause the mind to change. Moreover, the mind's self-knowledge is not fundamental: it cannot know its own thoughts better than it knows the ways in which its body is acted upon by other bodies. Further, there is no difference between contemplating an idea and assenting to it, and there is no freedom of the will at all. Sensory perception, which Spinoza calls "knowledge of the first kind", is entirely inaccurate, since it reflects how our own bodies work more than how things really are. We can indeed have accurate knowledge, but only of knowledge of truths that apply to all things (e.g., knowledge of geometry and physics, "knowledge of the second kind"), and knowledge of particular things seen as following from the nature of extension or thought (intuitive knowledge, "knowledge of the third kind"). In the third part of the Ethics, Spinoza argues that all things, including human beings, strive to persevere in their being. This is usually taken to mean that things try to last for as long as they can. Spinoza explains how this striving ("conatus") underlies our emotions (love, hate, joy, sadness and so on). The fourth part argues that human beings are controlled chiefly by such emotions. This condition is best remedied when we join with like-minded individuals into societies that promote clear reasoning. The fifth part argues we can defeat the emotions by replacing them with adequate ideas, and to the extent that we have adequate ideas, we do not die, since the portion of one's mind that contains such ideas is eternal.