Full Idea
The non-graspable presentation is either not from an existing object or from an existing object but not in accordance with it; it is neither clear nor well stamped (i.e. distinct).
Gist of Idea
Non-graspable presentations are from what doesn't exist, or are not clear and distinct
Source
report of Stoic school (fragments/reports [c.200 BCE]) by Diogenes Laertius - Lives of Eminent Philosophers 07.46
A Reaction
This sounds exactly like Locke's account of secondary qualities, at least as interpreted by Peter Alexander. That is, they are genuine qualities of things, but misleading, in a way that primary qualities are not.
Book Reference
'The Stoics Reader', ed/tr. Inwood,B/Gerson,L.P. [Hackett 2008], p.12
Related Idea
Idea 20780 Graspable presentations are criteria of facts, and are molded according to their objects [Chrysippus, by Diog. Laertius]