Full Idea
There are two kinds of opinion: one is assent to something which is not graspable; the other is weak belief.
Gist of Idea
Two sorts of opinion: either poorly grounded belief, or weak belief
Source
report of Stoic school (fragments/reports [c.200 BCE]) by John Stobaeus - Anthology 2.11m
Book Reference
'The Stoics Reader', ed/tr. Inwood,B/Gerson,L.P. [Hackett 2008], p.149
A Reaction
Strong belief usually qualifies as knowledge. The Greek 'opinion' and 'belief' don't exactly map onto the modern words. This idea covers both the subjective aspect of belief (its strength) and its objective aspect (its grounding).