Chronologically, De Oratore and De Re Publica (of which the Somnium was the conclusion) fall just after Pro Caelio, in the years just before the Civil War. It is clear that Cicero turned to philosophical (Platonic) dialogue as a form at least in part as the result of his political frustration: he was effectively banned from a major role in public life, and chose to contribute to Roman culture by other means. That it is a deliberate contribution is clear from the prefaces to both works as well as from Cicero's correspondence (for C.'s own explanation of his actions during this period (55-51), you could look at his long letter to Lentulus, ad Familiares I 9). They are also, without much doubt, his stylistic masterpieces: the opening paragraph of De Oratore in particular is an extraordinary piece of writing, and not at all easy.

Since I have been studying these texts for a very long time, I find it frustrating to assign relatively small sections--the opening of one dialogue and the end of the other. If you have the time (which you don't), you should look at the new translation of De Oratore by James May and Jacob Wisse, which has a good introduction to the rhetorical theory in particular. Aside from that, you should consider the two assigned excerpts in rather different ways:

1. De Oratore. Look in particular at

a) The ways in which C. sets up parallels between himself and his brother Quintus on the one hand and the protagonists of the dialogue, Crassus and Antonius, on the other. This includes not only their attitudes towards rhetoric and culture, but the dramatic situation of Crassus and Antonius and the real situation of Cicero himself.

b) The development of the dramatic setting: what does it show about Cicero's relationship to Plato? His ideas about Roman social and political life? about otium and negotium?

2. Somnium:

a) Again, Cicero's relationship to Plato. If the Myth of Er in Republic 10 is not fresh in your mind, have a look at it. What qualities in human life lead to immortality? What does the universe look like? What is the role of gloria and uirtus?

b) This time, look also at C.'s relationship to Lucretius. Look back at Lucretius' proem, in particular the dream of Ennius.

Some bibliography. Since I am already assigning my own edition of the Somnium, I might as well add more of me. Don't feel obliged to agree: I have my own perspective (which may be familiar already), and you don't need to accept it. I am putting two articles in a folder in 617 for your edification:

"De re publica and De rerum natura" (from Style and Tradition, 1998)

"Plato with Pillows: Cicero on the Uses of Greek Culture" (forthcoming in a volume in honor of T.P. Wiseman, 2002).