Though Cassius may be duplicitous, self-serving, and power-hungry, he is a cunning conversationalist and a highly affective speaker. In Act 1, Scene 2, as Cassius attempts to bring Brutus into his conspiracy against Caesar, he pays careful attention to Brutus's doubts and incorporates them into his argument. Using the rhetoric of logos (appeal to reason), and laying the foundations of his case on and a reasonable appeal to Brutus's sense of honor, Cassius recruits Brutus to his cause.
For let the gods so speed me as I love
The name of honor more than I fear death.
I know that virtue to be in you, Brutus,
As well as I do know your outward favor.
Well, honor is the subject of my story.
I cannot tell you what you and other men
Think of this life; but, for my single self,
I had as lief not be as live to be
In awe of such a thing as I myself.
When Cassius hears that Brutus is chiefly concerned with honor above all else, he begins to craft a careful critique of Caesar that resounds with Brutus’s anxieties. On the fly, Cassius makes honor “the subject” of his story and lays out a logos-driven case for the importance of honor to himself and, further, to the cause at hand. Later, Brutus himself will rely on logos to explain his reasoning for assassinating Caesar to the crowd of plebeians that assembles after his death.
By displaying Cassius's versatility as a debater, and his ability to adopt the reasoning methods and argumentation best suited to sway his listener, Shakespeare establishes him as a particularly cunning antagonist and furthers the lengthy exploration of the power of persuasive speech and the dangers of succumbing to sweet-talking found throughout Julius Caesar.
In Act 3, Scene 2, Brutus addresses the assembled crowd after Caesar's death. He uses the rhetorical device of logos to explain the reason for the conspiracy against Caesar that has led his assassination.
Romans, countrymen, and lovers, 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. Censure me in your wisdom,
and awake your senses that you may the better
judge. If there be any in this assembly, any dear
friends of Caesar’s, to him I say that Brutus’ love
to Caesar was no less than his. If then that friend
demand why Brutus rose against Caesar, this is my
answer: not that I loved Caesar less, but that I loved
Brutus’s major flaw in speaking to the Romans after Caesar’s death—the flaw that enables Antony to seize the moment and turn the crowd against him—is that he attempts to reach the crowd through reason and reason alone: laying out a cost-benefit analysis, he determines that he loves Rome more than Caesar and therefore must act in defense of Rome. This logos-driven justification appeals to the audience's sense of logic, and, accordingly, Shakespeare structures the speech in prose to match Brutus's matter-of-fact tone.
Shortly hereafter, Brutus will find that his words fall short of fully swaying the crowd when Antony ascends the dais and delivers his rousing call-to-grief in honor of his fallen friend. Julius Caesar presents a stark warning against the kind of clinical calculations that Brutus makes in this speech, and as Shakespeare pits this logical use of language against Antony's rhetoric of pathos, it is clear that an emotional appeal is more effective at swaying the favor of a crowd.