Summary: Ethics (page 6)

As a result, affects arise and disappear according to the same necessity as things and events. A science of affects is therefore possible: I will consider human actions and appetites as if they were lines, planes, or bodies ¹.

Among the definitions that open Part III, one stands out:

By affect, I mean the affections of the body that increase or decrease the body's power to act, together with the ideas of these affections ².

The first proposition defends the idea that our mind acts insofar as it has adequate ideas and undergoes passion insofar as it has inadequate ideas. An adequate idea, according to Spinoza's definition in Part II, is an idea which, in itself and without relation to its object, possesses the intrinsic properties or denominations of a true idea ³.

Can we simply say that an adequate idea is a true idea? Probably. However, Spinoza's formulation suggests rather that an adequate idea is a well-formed idea—one that possesses the structure and properties of a true idea.

The corollary of this first proposition is remarkable: The mind is subject to passions in proportion to the number of inadequate ideas it possesses; conversely, it acts in proportion to the number of adequate ideas it has ⁴. Can we infer from this that a mind which attains the highest truths would be pure action?

We have seen in Part II Spinoza's critique of the faculty of will and his assertion that body and mind are one and the same thing, viewed from two different perspectives.

This is why Spinoza reminds us that the body cannot determine the mind to think, nor can the mind determine the body to movement, nor to rest, nor to anything else ⁵.

What determines a particular movement of our body is not the mind but a preceding movement of another body—or God, conceived as an extended substance. Similarly, a thought can only have as its cause another preceding thought—or God, conceived as a thinking substance.

Thus, the order or sequence of things is one and the same, whether we conceive of nature under one attribute or the other. In other words, the order of the actions and passions of our body follows by nature the same order as the actions and passions of our mind ⁶.

It is therefore a mistake to believe, as is commonly assumed, that the body moves under the impulse of the mind. Moreover, the body can move without the mind, as sleepwalkers demonstrate. Finally, no one truly knows what the body is capable of: Experience has taught no one so far what the body can do by the laws of nature alone ⁷.

Do we believe that the body is inert without the mind? Spinoza counters this with the example of sleep: if the body were inert, then so too would be the mind.

Spinoza once again develops a critique of the will, or free will, which is irreconcilable with the fundamental determinism of his thought:

Thus, the infant believes it yearns freely for milk, the angry child thinks it desires vengeance, and the coward believes it flees of its own accord. The drunken man believes that it is by a free decree of the mind that he speaks words which, once sober, he wishes he had kept silent—when in reality, he was unable to restrain the impulse that drove him to speak ⁸.

To summarise: Men believe themselves to be free solely because they are conscious of their actions and ignorant of the causes by which they are determined ⁹.

The famous Proposition 6 establishes the principle of conatus:

Everything, insofar as it is in itself, strives to persevere in its being ¹⁰.

Indeed, every thing resists whatever might threaten to suppress its existence. This effort—this fundamental tendency inherent in every being—is nothing other than the will (when considered from the perspective of the mind) or desire (when considered from the perspective of both mind and body).

¹ ibid.
² III, definition 3
³ II, definition 4
⁴ III, prop.1, corollary
⁵ III, prop. 2
⁶ ibid., note
⁷ ibid.
⁸ ibid.
⁹ ibid.
¹⁰ III, prop.6