This is the classic "Julius Caesar" question and I'm not sure how many millions of essays have been written about it! I'll just start you off with the major points which you can then develop:
- Brutus' speech is hugely rhetorical, with a particular emphasis on antithesis (where one word is "set against" another word to create a balanced effect). Read aloud the following quote (my emboldenings) and ask how natural it sounds:
- Hear me for my cause and be silent, that you may hear. Believe me for mine honor, and have respect to mine honor, that you may believe.
- Brutus' speech is very, very patterned, and formal. It doesn't sound, in short, at all like he is making it up on the spot. This fits with the high-minded idealism of the speech itself, which often has Brutus referring to himself in the third person, and which argues that Brutus' murder of Caesar was actually nothing to do with Caesar himself, but everything to do with Rome. "Not that I loved Caesar less, but that I loved Rome more."
- Antony, who famously begins by addressing his audience as "Friends" is far more colloquial, and the audience interrupt/respond to his speech throughout (unlike Brutus, who delivers it, it seems, in silence).
- Antony's speech uses an insinuating irony - "Brutus is an honorable man" starts off sincere, and, the more it is repeated, the more ironic it becomes. The speech takes hold gradually.