Our friend Liberalis is now downcast; for he has just heard of the fire which has wiped out the colony of Lyons. Such a calamity might upset anyone at all, not to speak of a man who dearly loves his country. But this incident has served to make him inquire about the strength of his own character, which he has trained, I suppose, just to meet situations that he thought might cause him fear. I do not wonder, however, that he was free from apprehension touching an evil so unexpected and practically unheard of as this, since it is without precedent. For fire has damaged many a city, but has annihilated none.
The opening establishes the scale. A whole city, in one night. Liberalis has been training his character to meet fearable things — fires, illness, loss of fortune — and is now meeting something he had not specifically rehearsed.
Therefore, nothing ought to be unexpected by us. Our minds should be sent forward in advance to meet all problems, and we should consider, not what is wont to happen, but what can happen.
We should therefore reflect upon all contingencies, and should fortify our minds against the evils which may possibly come. Exile, the torture of disease, wars, shipwreck,—we must think on these. Chance may tear you from your country or your country from you, or may banish you to the desert; this very place, where throngs are stifling, may become a desert. Let us place before our eyes in its entirety the nature of man's lot, and if we would not be overwhelmed, or even dazed, by those unwonted evils, as if they were novel, let us summon to our minds beforehand, not as great an evil as oftentimes happens, but the very greatest evil that possibly can happen. We must reflect upon fortune fully and completely.
This is the formal statement of praemeditatio malorum — meditation on coming evils — as the central practice of the discipline of desire. Not anxious rehearsal. Deliberate consideration, performed when calm, so that when the disruption arrives it arrives as an expected guest. The aphorism most often quoted from this letter — "he robs present ills of their power who has perceived their coming beforehand" — is a paraphrase, not Gummere's wording, but it captures the move precisely. The reason to rehearse is not to suffer in advance. It is to dissolve the surprise that gives suffering its sharpest edge.
The closing move is the one Seneca only implies in this letter but states explicitly elsewhere (notably Letters 13 and 78): the fire that took Lugdunum was a real loss; the damage it has done to Liberalis's spirit is a separable thing — shaped not by the fire but by the judgments Liberalis grants to the impression of it. The praemeditatio is the work of preparing those judgments in advance.
Seneca, Moral Epistles to Lucilius Letter 91 (sections 1, 4, 8) · trans. Richard M. Gummere (1917)
Context
Written in 64 CE by Seneca, after the city of Lugdunum (modern Lyon) burned to the ground in a single night. Seneca's friend Liberalis is from there. The letter is the great Stoic statement of praemeditatio malorum — written in the wake of a catastrophe that, on Seneca's own argument, should have been less surprising than it was. Behind the practice sits the Stoic doctrine of heimarmenē: the chain of causes that, in principle, could bring about the very greatest evil that possibly can happen.