Here's a longer excerpt from Brutus:
sed ea in nostris inscitia est, quod hi ipsi, qui in Graecis antiquitate delectantur eaque subtilitate, quam Atticam appellant, hanc in Catone ne noverunt quidem. Hyperidae volunt esse et Lysiae. Laudo. sed cur nolunt Catones? . . . Cur igitur Lysias et Hyperides amatur, cum penitus ignoretur Cato?
As Calgacus notes, hanc
refers back to antiquitate
, and, in the original, despite being singular, to ea subtilitate quam Atticam appellant
, "that plainness/simplicity/absence of ornament that they call "Attic." See Lewis and Short, subtilitas
The puzzle here is what Cicero means by antiquitate
. The omitted words are a clue to what Cicero is talking about. He uses the term antiquitas
(as the omitted words demonstrate) to mean the older, "Attic" style of rhetoric, which was plain and unadorned, but could be very effective in the hands of Lysias or Hyperides.
The quod clause is a substantive clause which is in apposition to ea inscitia
. Allen & Greenough 572:http://www.perseus.tufts.edu/hopper/text?doc=AG+572&fromdoc=Perseus%3Atext%3A1999.04.0001
Cicero is saying that Cato's speeches have the same qualities of unadorned brevity and concision as Greek orators such as Lysias and Hyperides, who exemplify the older "Attic" style of oratory, but there is ignorance among contemporary Roman orators in that even those who take pleasure in that style (which Cicero refers to as antiquitas
) in Greek literature haven't even recognized it [noverunt
] in Cato. He goes on: "They want to be a Hyperides or a Lysias [literally, Hyperideses and Lysiases]. I'm all for it. But why don't they want to be a Cato? . . . Why are Lysias and Hyperides so well-loved, when Cato is completely unknown?"
Hope this helps.