In my previous Spinoza writings, I talked a lot about our brains having a distinct structure and our mental life being the self-maintenance of that structure. Spinoza doesn't teach us much—or if he does, it's not in a way that I can understand....
So is he an existentialist? I don't know. I've never really understood what that means. But if we take it as meaning that we are alone in the universe and there is no God or afterlife, then certainly yes.
Spinoza claims that the mind is an idea (or, more precisely, II 15, a composite of many ideas, although it is more practical to use the singular number). The idea's object is the body "and nothing else" (II 13). From this follows that our mind is just as much a part of us as any other idea-composed thing such as a stone or a tree. It is therefore possible for someone else to get a glimpse into our mind - if we let them - by examining how we act and what effects we have on others.
However, since the mind is an idea, it cannot be perceived with the senses. Instead, we must rely on reason to grasp it. Reason allows us to understand that our mind affects our body and thus concludes that we cannot exist without it.
Furthermore, reason also tells us that we cannot will ourselves into existence nor can we destroy ourselves. This implies that we are responsible for what we do with our minds and that we can change whatever state of mind we want to change. With reason as our guide, we can learn how to control our mind and use it to our advantage.
In addition to reason, imagination helps us comprehend things that cannot be sensed by the senses. For example, when looking at a sunset, we not only see colors but also feel heat from the sun's rays and smell smells in the air.
The mind is subject to a different property than the body, which is subject to the rules of nature. Spinoza admits that humans are free in the sense that they may substitute another thinking for a given moderate urge, but he maintains that overwhelming wants (as in violent emotions) cannot be resisted. Therefore, the mind is not free in the rational sense.
People who lack reason and experience are unable to use their freedom intelligently, which means that they are slaves. For Spinoza, there is no such thing as a natural slave because everyone is free to follow their own inclinations.
In conclusion, the mind is part of the human essence and it is free.
Spinoza asserts that the intellect and body are indistinguishable. However, he asserts that the mind thinks but does not move, whereas the body moves but does not think. Thus, it is possible to have mental activity without any physical movement.
He also states that "the human mind is a product of nature." This means that just as much as the earth's environment shapes who we are, so too does our mind-it's merely another part of the natural world-shape who we can be.
Finally, he says that "God is absolutely infinite," which means that he or she has no limits whatsoever. In other words, there is no height that God cannot reach, no width that God cannot embrace.
Thus, Spinoza claims that the intellect and body are indistinguishable. He also says that "the human mind is a product of nature." Finally, he claims that "God is absolutely infinite," which means that there are no limits to his or her power or knowledge.
These are just some of the views that can be found in Ethics.
Spinoza's (IIIp7) argument that the essence of every finite mode, including any human mind (IIIp9), is a yearning (conatus) to persist in existence is an attempt to provide an account of nature in which human beings with their seeming idiosyncrasies are natural. He argues that since all natural things exist in order to persevere in their being, then we too have this aim.
In fact, for Spinoza, there is only one kind of thing in nature: modes. A mode is anything that exists in reality, whether a person, a tree, or a stone. It is not necessary that a mode be material; for example, thought and emotion are modes of action. However, most modes are physical objects such as people or animals, but not all physical objects are modes. For example, a table cannot itself affect other things to bring them about, so it cannot be considered a mode. However, a mental state can cause another mental state or physical effect (such as pushing a button), so it can be considered a mode.
Since all modes exist in order to persevere in their being, they must continue to exist even if they are not being affected by other things. Therefore, they must have within themselves the power to preserve themselves. This power that some modes have over others is called "finite ness". Only modes that have this finite ness can hope to survive beyond their creator.