Full Idea
Stoics distinguish matter and substance; they say that matter is that which underlies those things which have qualities; however, the primary matter of all things or their most primeval foundation is substance, which is without qualities and unformed.
Gist of Idea
Stoics say matter has qualities, and substance underlies it, with no form or qualities
Source
report of Stoic school (fragments/reports [c.200 BCE]) by Chalcidius - Commentary on Plato's 'Timaeus' 290
Book Reference
'Hellenistic Philosophy: Intro Readings', ed/tr. Inwood,B. /Gerson,L. [Hackett 1988], p.123
A Reaction
In this account, substance begins to sound like Kant's 'noumenon', which is a theoretical concept which has retreated beyond all experience. Stoics were under pressure to cover everything for which the Atomists offered explanations.