Full Idea
Stoics say there are two elements in the cosmos, cause and matter. Matter lies inert and inactive, a substance of unlimited potential, but destined to remain idle if no one sets it in motion; it is cause (the same as reason) that fashions matter.
Gist of Idea
The cosmos has two elements - passive matter, and active cause (or reason) which shapes it
Source
report of Stoic school (fragments/reports [c.200 BCE]) by Seneca the Younger - Letters from a Stoic 065
Book Reference
Seneca: 'Letters from a Stoic (Selections)', ed/tr. Campbell,Robin [Penguin 1969], p.118
A Reaction
[compressed] It take this to be anti-essentialist, because the point of a scientific essence is to be the source of the activities and structures of the matter. Seneca must think matter lacks essence, in order to be moulded like this. Note 'unlimited'.