Foreword: as an Italian student, I hope that I will not make many mistakes in translating the lexicon from my native language to English; sometimes this will happen, and so putting the Italian word in curved braces seems to me the best thing to do to avoid confusion or misinterpretation.
Trying to understand stoic thought (especially stoic logic), I came across the doctrine of anticipation, which is the foundation for discussing stoic nominalism.
I understood that all the representations (rappresentazioni, from the greek phantasia kataleptiké) given by things from the real world leave a sign into the soul; after the representations disappear, what remains is a set of remembrances which, if the representations was of the same kind, is called "experience" (esperienza). The concepts arise from experience by a natural process called anticipation or common concept (nozione comune, form the latin communes notitiae, or from the greek prólepsis).
At this point, my textbook (1) says that
"anticipation is the natural concept/notion of the universal" (or "l'anticipazione è la nozione naturale dell'universale"), from Diog. L, VII, 54.
From there the author starts talking about individual reality, and says that the universal exists only in anticipations, making stoic thought a form of nominalism.
The thing that I don't get is what does it mean for the prólepsis to be the natural notion/concept (nozione naturale) of the universal.
(1) Storia della filosofia, Volume 1; N. Abbagnano; UTET.