Full Idea
The Stoics declare that there is a difference whether a thing is of such a kind that something cannot be effected without it, or such that something must necessarily be effected by it.
Gist of Idea
Some facts are indispensable for an effect, and others actually necessitate the effect
Source
report of Stoic school (fragments/reports [c.200 BCE]) by M. Tullius Cicero - On Fate ('De fato') 16.36
Book Reference
Cicero: 'On Fate, Stoic Paradoxes, Oratory', ed/tr. Rackham,H. [Harvard Loeb 1942], p.233
A Reaction
This points out that causal preconditions can be either necessary or sufficient for their effect. Because it is a very perceptive point, I surmise that it originated with Chrysippus.
Related Idea
Idea 13309 That something is a necessary condition of something else doesn't mean it caused it [Seneca]