In William Shakespeare's play "Julius Caesar," Brutus is more of a philosopher motivated by idealism, while Cassius is a practical man guided by politics and power. Unlike Brutus, who genuinely believes in the virtues of republicanism and the dangers of autocracy, Cassius just uses republican rhetoric for his political gain.
Although Brutus truly loves Caesar, he is deeply disturbed by Caesar's increasing power. Because Brutus's progenitor was famous for ridding Rome of a tyrant, he feels a strong personal connection to republicanism and believes that he must act to prevent Caesar from becoming king of Rome. Guided by his moral code, he fails to take advantage of key political moments. For example, in Act 3, scene 1, he allows Antony, one of Caesar's supporters, to speak over Caesar's body even though the other conspirators know that allowing Antony to speak is potentially dangerous. Antony himself praises Brutus' virtue in his final speech.
Cassius plays on Brutus' virtue to involve him in the conspiracy against Caesar. Knowing that Brutus wishes to live up to his family's heritage, Cassius writes notes to Brutus that ostensibly come from various Roman citizens asking for Brutus to do something about Caesar's increasing autocracy. Cassius does not have a strong moral compass. He wants to deny Antony's right to speak, and he even participates in bribery schemes after the assassination. These schemes anger the strictly moral Brutus, who says that Cassius's actions mar their pure cause.