There is a moment, somewhere between the second and third hour awake, when the day declares what it is going to be. Not through any event. Through something closer to weather in the chest: a lift, or its absence. Spinoza, who ground lenses in The Hague and died at forty-four with his great book unpublished, gave that weather a name and made it the hinge of an entire metaphysics. Conatus: each thing strives, so far as it lies in itself, to persevere in its being, and this striving is nothing other than the thing's actual essence. Not a drive the thing has. The thing itself, considered as verb.

What makes this more than seventeenth-century vitalism is what he does next, in the third and fourth parts of the Ethics, with a coldness that still reads as scandalous. Good and evil are not properties of the world. They are names for what happens to our power of acting. Whatever increases it, we call good; whatever diminishes it, evil. Joy is the passage to a greater perfection, sadness the passage to a lesser. There is no independent moral firmament against which our lives are measured and found wanting. There is only the local question, answered by the body before the mind gets to it, of whether we are becoming more capable of what we are.

I find I cannot read this without flinching slightly, and the flinch is worth examining, because it is where the essay actually begins. We were raised, most of us, in the long shadow of a morality that stands outside us and judges. Spinoza takes it away and hands us something that feels at first like a licence and only later like a burden. If good is what enlarges my power of acting, then I am responsible for knowing what enlarges it. And here is the trouble I want to sit with rather than solve: I do not think I know. I do not think we know. We have become a species remarkably poor at reading its own increase.

Consider what the feed does, and I mean this precisely, not as complaint. It offers a passage that registers in the body as joy: the lift of the notification, the small warmth of being addressed, the sense of a widened world. Spinoza's criterion, taken naively, would file it under good, because something in me has been raised. But he was more careful than that. The whole architecture of the Ethics turns on the distinction between the passions, which are affects whose cause lies outside us and of which we have only confused ideas, and the actions, which follow from our own nature adequately understood. Both feel like life. Only one is the increase of a power that is mine. A body raised by a cause it cannot see has not become more capable; it has become more moved.

This distinction is doing more work now than it did in 1677, because we have built, for the first time in the history of the animal, institutions whose own conatus runs on ours. A platform strives to persevere in its being exactly as a rock or a wolf or a grieving man does; it is a thing, it has an essence, and its essence is expressed as an effort to continue. The uncomfortable elegance of Spinoza's system is that it grants this without hesitation. There is no special pleading for the human. Everything that is, insofar as it is, strives. Which means the question of our age is not whether corporations are persons, that legal decoy, but something harder: what happens when one thing's persistence is metabolically dependent on the confusion of another thing's affects. Not on our suffering. On our not being able to tell.

Spinoza would call this bondage, and he means it technically. Servitus: the condition of a mind governed by affects whose causes it does not understand, tossed like waves by contrary winds, ignorant of its own fate. He thought the exit was knowledge. Adequate ideas of the causes of our affects convert passion into action; the affect does not vanish but it ceases to be suffered, because it has been understood. This is the most hopeful proposition in seventeenth-century philosophy and possibly the most naive, and I want to be honest that I cannot decide which. Has understanding the mechanics of the scroll ever once released anyone from it? I know the design pattern. I know about variable reward schedules, I have read the studies, I could give the lecture. My thumb has not received the lecture.

So either Spinoza was wrong about the sufficiency of knowledge, or the knowledge we possess is not the kind he meant. I lean, tentatively, toward the second, because his word was not information. He distinguished three kinds of knowing, and the third, scientia intuitiva, is a knowledge that grasps a thing in a single motion as flowing from its cause, the way you do not calculate that a face is sad. Knowledge in that register is not something you have; it is something you have become. And we are extraordinarily well supplied with the first kind and starved of the third. We know about ourselves the way a man knows the specifications of a car he has never driven.

There is a strange corroboration from a direction Spinoza never anticipated. In 1944 the physicist Erwin Schrödinger published What Is Life?, arguing that the essential feature of an organism is that it feeds on negative entropy, maintaining its improbable order by exporting disorder into its surroundings. The formulation was refined through the twentieth century into a whole tradition of dissipative structures, Ilya Prigogine's work chief among it: the flame, the whirlpool, the cell, all of them patterns that persist only by continuous throughput. Persistence, at the level of physics, is not rest. It is a particular kind of restlessness that manages to hold its shape. Which is uncomfortably close to what Spinoza said about essence being effort, three centuries before anyone could have measured it.

But the physics also hands us a warning he could not have issued. A dissipative structure does not care what it dissipates. A flame will consume a house with the same fidelity to its own nature as it consumes a candle. Persisting, in itself, has no content; it is indifferent to what it persists as. And this is where I think our confusion actually lives. We have inherited a culture that treats the sheer fact of continuing as self-justifying: the startup that survives, the marriage that lasts, the body kept going, the career sustained through a decade of quiet diminishment. Endurance has become our substitute for a good we can no longer name. But Spinoza's conatus was never a defence of endurance. It was an argument that the striving has a direction, toward greater power of acting, and that a life which continues while its capacity narrows is not persevering in its being. It is being ground down slowly enough to be mistaken for stability.

What would it mean to take the criterion seriously, on an ordinary Tuesday? Not the ecstatic version, not the retreat or the reinvention, but the small forensic question: has my power of acting increased today, or have I merely been moved? I notice, when I ask it honestly, that the answer often has nothing to do with pleasure. The conversation that cost me something and left me more able to think. The hour of difficulty in which nothing was enjoyed and something was acquired. Against these, the evenings of frictionless lift that left me, at their end, slightly less capable of my own attention than when they began. Spinoza's laetitia is not enjoyment. It is a transition, and transitions can be arduous, and the arduous thing is not thereby the enemy.

And yet I cannot make this into a rule, and I am suspicious of anyone who can. Because the criterion has a hole in it that Spinoza's own life illuminates without closing. He was excommunicated by his community at twenty-three, the cherem read aloud in the Amsterdam synagogue with its curses by day and by night, and he did not fight it or return. He lived alone, corresponded, declined a professorship at Heidelberg to protect his freedom of thought, and wrote a book which he knew could not be published while he lived. Was that an increase in his power of acting? He would have said yes, without theatre: solitude and refusal made him more fully the thing he was. But it would have looked, from any window on the Paviljoensgracht, exactly like a man being diminished. From the outside, the two are not distinguishable. Which means the criterion cannot be applied to another person, ever, and the whole liberal apparatus of measuring lives against each other collapses into silence, which is perhaps its correct destination.

What remains is a question I cannot get underneath, and I have been trying for some weeks. If my essence is my striving, and my striving has been substantially shaped by structures that persist by shaping it, then whose effort am I when I persevere? Not a paranoid question. Spinoza has no room for a self standing behind its affects, uncontaminated, choosing. There is only the striving, and it is already the product of everything acting on it. The mystic's answer and the materialist's answer converge unnervingly here: there was never a separate me to be captured, and so nothing has been stolen. But something has been bent, and the bending is felt, and the feeling is the only instrument we have and it is the instrument that has been bent.

So I keep returning to the moment before the day declares itself, the weather in the chest, and asking not whether it is joy but what it is joy at. Not what I want. What in me is doing the wanting, and whether it is still, in any sense I could defend, mine.