Most of the affects defined in Part III of the Ethics come in pairs: for each affect there tends to be a joyful and a sad variant. Love and hate offer the simplest example of this: love is just joy accompanied by the idea of an external cause; hate is just sadness accompanied by the idea of an external cause. There are more complicated couplets, too. For instance, ‘The striving to do evil to him we hate is called Anger [ira]; and the striving to return an evil done us is called Vengeance [vindicta]’ (IIIP40c2s) — this finds its counterpart in that ‘reciprocal Love, and consequent striving to benefit one who loves us, and strives to benefit us, is called Thankfulness, or Gratitude [gratia seu gratitudo]’ (IIIP41s). In general, affects are ideal relations we form toward ourselves and toward others that involve our imagination; and since these relations can be either joyful or sad, it’s obvious why they would come in pairs.
But they do not always appear in such neat symmetrical form. In particular, consider the scholium to III P26:
Pride [superbia], therefore, is Joy born of the fact that a man thinks more highly of himself than is just. And the Joy born of the fact that a man thinks more highly of another than is just is called Overestimation [existimatio], while that which stems from thinking less highly of another than is just is called Scorn [despectus].
So, one can think too highly of oneself (pride) and of others (overestimation); and one can too lowly of others (scorn). But this is obviously three-quarters of a pair of pairs. There’s a conspicuous absence here: Spinoza does not say that it is possible to think less highly of oneself than is just. As it happens, this is no accident.
In order to see why, it’s important to consider what the point of this part of the Ethics is; you have to keep in mind what we gain by undertaking an analysis of affects. One of the first claims Spinoza makes in Part III of the Ethics is that the common conception of free human volition is untenable. Human beings, he tells us, tend to be conscious of their appetites, their desires, and their actions — and, at the same time, they tend not to be conscious of the causes that determine them to desire and to act the way they do. There is, if you like, an epistemic gap that gives rise to the misconception that we freely choose the things we desire and will: we are aware that we have desires, but are unaware of the reasons why we have these desires. Basically, then, Spinoza identifies an informal fallacy underlying most of our intuitions about human free will: from the (negative) absence of knowledge of the causes that determine us to act, we infer the (positive) claim that our wills and actions really have no causes; and so, if we act in a certain way (and we do!), it must be because we freely chose to do so. But this is an argumentum ad ignorantiam, an argument from ignorance. It is exactly as valid as saying that because I do not know why the sky is blue, therefore there is no reason why the sky is blue; and it is even a bit weirder than that, because we don’t usually attribute to the sky the freedom to choose to be blue.
In this context, we can see what the value is of Ethics III: Spinoza is giving us an account of how our desires are determined, even though we may not be conscious of these processes of determination. His claim is that when our desire is configured in a particular way, we are necessarily led to act in accordance with that desire. And affects very significantly modify or shape our desires, almost always through the imagination.
Let’s consider a very simple example.
I experience joy — that is, my power to think and to act increases in some way, and I am conscious of this increase. Now, I imagine that something external to me is the cause of my joy; let’s say I imagine that my joy is caused by some one person in particular, Rho. That is, I love Rho! This is nice. Now when you love someone or something, this determines you to act in a particular kind of way toward them: namely, you will strive to aid them, to encourage them, to try to increase their power to think and to act. If you like, you can cash this out in a utilitarian sort of way: since I imagine that Rho’s tendency is to bring me joy, increasing their power should, hypothetically, bring me even more joy. But Spinoza doesn’t limit himself to this kind of account; simply put, it just necessarily follows that I strive to aid what I love. And since I love Rho, that’s just what I am determined to do.
Now notice the work done by imagine in that last paragraph. 1. I imagine that Rho is the cause of my joy. But I might be wrong about this. For one thing, maybe I’m just totally mistaken about where my joy is coming from, and Rho is in fact indifferent to that process; maybe they just have nothing to do with my joy at all. But it might even be worse than that: Rho’s nature might be such that their tendency is actually to decrease my power to act and think. But no matter: I can still imagine that they are the cause of my joy, and love them. And when I do, I am determined to do what I imagine will increase their power. So then: 2. I imagine that acting in a certain way will increase their power. But I may be wrong about that, too! The actions that I imagine here might not even affect Rho at all; if they do affect Rho, my actions might not increase or decrease Rho’s power in any way; or, again, worse case scenario, perhaps my actions will turn out to affect Rho negatively, so that their power to think and to act decreases. In a way, Spinoza’s point is that none of this matters: the relations that I imagine obtain between Rho and my joy, and the relations that I imagine will obtain between Rho’s capacities and the actions that I may perform, determine me to act in a certain and determinate way: I love them, so I necessarily strive to do what I imagine will increase their power. So we can see that Ethics III is really about the power of the imagination, or inadequate knowledge, to determine the will to desire certain things, and thereby to determine us to strive to act accordingly.
Let’s return, then, to the missing fourth affect that would complete our triplet of pride-overestimation-scorn. Pride: I experience joy from thinking myself more highly than is just. Overestimation: I experience joy from thinking of others more highly than is just. Scorn: I experience sadness from thinking less highly of others than is just. But what is the than is just, here? Evidently, it refers to the power of the thing being evaluated, since a singular thing’s essence just is its striving to persevere in its being. And the gap here is between the actual power of the thing and the power that I imagine it to have. So in pride, I imagine that I am more powerful than I really am, and this thought produces a joy in me. And in scorn, I imagine that someone is less powerful than they really are, and this thought produces a sadness in me. And remember that joy and sadness just are the conscious passage to a greater or lesser perfection — that is, consciousness of an increase or decrease in power.
So now we can see why the fourth category is missing. Let’s say that I imagine I have less power than I really have. This doesn’t happen abstractly; it happens concretely, taking the form of: I think I cannot do x (although x really is within my power). But this thought produces a sadness in me, it decreases my power — to what extent? Precisely to the extent that it removes x from my power. Why? Because the thought that I cannot do x determines my striving in a very particular way: it determines me not to try to do x, since I imagine that it is impossible for me to do so, and you cannot strive to do what you really think is impossible. And if I am determined not to do something, indeed not even to try, this is the same as it really not being within my power. I think that something is not within my power; I am determined necessarily to strive to do things other than this, which I think is impossible.
‘Indeed, no one thinks less highly of himself than is just, insofar as he imagines that he cannot do this or that. For whatever man imagines he cannot do, he necessarily imagines; and he is so disposed by this imagination that he really cannot do what he imagines he cannot do. For so long as he imagines that he cannot do this or that, he is not determined to do it, and consequently it is impossible for him to do it.’ (E III def.aff. XXVIII exp.)
You cannot underestimate yourself! You can only make things that would otherwise be in your power impossible for you. And remember, nobody knows what a body can really do.