Summary: Ethics (page 4)

If man thinks, he is not a substance but the essence of man is constituted by precise modifications of the attributes of God, something which is in God, and which without God can neither be nor be conceived, in other words an affection which expresses the nature of God in a precise and determined way ¹.

We can thus see that Spinoza differs fundamentally from Descartes on this point, for whom man is formed of two substances, the thinking substance and the extended substance.

For Spinoza, the human mind is not a substance, but a part of God's infinite intellect ². This allows this beautiful affirmation: God constitutes the nature of the human Spirit ³.

The body on the other hand is the object of the idea constituting the human mind or a manner of the Expanse precise and existing in act, and nothing else ⁴.

This conception makes it possible to give a solution to the problem of the union of body and mind that is fundamentally different from that of Descartes.

First of all, there is indeed union: That the Spirit is united to the Body, we have shown from the fact that the Body is object of the Spirit ⁵.

Then there are not two distinct things, but one and the same thing, considered from two different points of view:

The idea of the Body and the Body, i.e. the Mind and the Body, is one and the same individual, which we conceive sometimes under the attribute of Thought, sometimes under that of Extent ⁶.

This resolutely innovative solution to the mind-body problem leads Spinoza to reconsider the nature of two faculties: knowledge and will. Traditionally, both faculties are understood as involving both body and mind.

Philosophers have long debated the role of the body in the process of knowledge. How do we come to know something? At least initially, through bodily perception.

For Spinoza, we perceive external things through the senses and form universal concepts based on them. However, the senses present these things to us in a fragmented and confused manner, without order for the intellect: The senses present things in a mutilated and confused way, and without order for the intellect. ⁷ This is why this first kind of knowledge is imperfect: I am accustomed to call such perceptions knowledge from the mere suggestions of experience. ⁸

This first kind of knowledge encompasses what is commonly referred to as opinion or imagination.

It is the sole source of falsehood.

Knowledge of the second kind refers to reason—that is, the grasp of common notions and the formation of adequate ideas concerning the properties of things.

Knowledge of the third kind is intuitive science, which proceeds from the adequate idea of the formal essence of certain attributes of God to the adequate knowledge of the essence of things ⁹.

These last two kinds of knowledge are necessarily true.

The truth of an idea is revealed in its self-evidence: Whoever has a true idea knows at the same time that he has a true idea and cannot doubt the truth of the thing ¹⁰.

Since our mind is a part of God's infinite intellect, the truth of our clear and distinct ideas is just as necessary as the truth of God's own ideas: "It is just as necessary that the clear and distinct ideas of the mind should be true as it is necessary of the ideas of God ¹¹.

Reason perceives things as they are in themselves. It therefore grasps their necessity. Similarly, it is in the nature of reason to perceive things under a certain species of eternity ¹² -sub specie aeternitatis.

As a consequence of his new conception of the union of mind and body, Spinoza must also reconsider the traditionally accepted notion of will. The will is classically understood as the faculty by which the mind acts upon the body. But if body and mind are one and the same thing, merely considered from two different perspectives, what then is the will?

¹ Book II, prop.10, corollary
² II, prop. 11, corollary
³ ibid.
⁴ II, prop. 13
⁵ II, prop. 21, demonstration
⁶ II, prop.21, note
⁷ II, prop. 40, note II
⁸ ibid.
⁹ ibid.
¹⁰ II, prop. 43
¹¹ ibid., note
¹² II, prop. 44, corollary 2