Full Idea
A proposition is what can be asserted or denied on its own, for example, 'It is day' or 'Dion is walking'.
Gist of Idea
A proposition is what can be asserted or denied on its own
Source
Chrysippus (fragments/reports [c.240 BCE]), quoted by Diogenes Laertius - Lives of Eminent Philosophers 07.65
Book Reference
'The Stoics Reader', ed/tr. Inwood,B/Gerson,L.P. [Hackett 2008], p.17
A Reaction
Note the phrase 'on its own'. If you say 'it is day and Dion is walking', that can't be denied on its own, because first the two halves must each be evaluated, so presumably that doesn't count as a stoic proposition.
Related Idea
Idea 13467 Leibniz was the first modern to focus on sentence-sized units (where empiricists preferred word-size) [Leibniz, by Hart,WD]