In recent excerpts, we have looked at passages relating to what is meant by the language about form, first from Plato, then Aristotle on Plato, and then Cicero on the path from Socrates through Aristotle, have been cited. There is nothing exhaustive about this inventory of excerpts, though they are helpful. Here, we look at Seneca.
Lucius Annaeus Seneca (4 B.C. — A.D. 65, usually simply known as “Seneca”, or else “Seneca the Younger” to distinguish him from his father, Lucius Annaeus Seneca the Elder) usually follows after Cicero (106 B.C. — 43 B.C.) in modern histories of Roman Stoic philosophy. Stoicism is, of course, Greek in its origins, but became a Latin inheritance, and was, perhaps, better suited to the temperament of Latin culture than was Platonism. The chronological priority Cicero enjoys in the Latin Stoic tradition, however, is overshadowed by the priority of influence that Seneca enjoys as a source for our knowledge of Stoic ethics , if not Stoicism itself. (Sadly, some significant sections of Cicero have been lost.) Stoicism is often touted as more practical, more pragmatic, than Platonism; perhaps accordingly, it may not come as a surprise to learn that the Stoic Seneca was, as is often noted, a senior advisor to the emperor Nero. He was forced to commit suicide in A.D. 65 because of his suspected involvement in plotting against the emperor; his Letters were likely written during retirement after A.D. 62.
Seneca was a rather eclectic Stoic, however. Arguments have been made to include him in the history of the Platonic tradition.  Certainly both his familiarity and engagement with the larger Greco-Roman philosophical tradition makes him fit to be included in this series of excerpts, which largely focus on Plato, and which are largely preparatory for other work here.