Why is Brutus upset with Cassius in Act 4?

Brutus becomes upset with Cassius in Julius Caesar because he believes Cassius has acted dishonorably by accepting bribes and protecting corrupt officers. Their argument happens in Act 4, when the conspirators are preparing for war against Antony and Octavius. Brutus reminds Cassius why they killed Caesar in the first place: “Did not great Julius bleed for justice’ sake?” He argues that if they assassinated Caesar to defend Rome from corruption, then they cannot now “contaminate” themselves with “base bribes.” Brutus even says, “I had rather be a dog, and bay the moon, / Than such a Roman.”

The conflict shows the difference between the two men’s values. Brutus is driven by strict moral principles and believes their cause must remain honorable. Cassius is more practical and politically flexible. Earlier in the play, Cassius wanted to kill Antony along with Caesar because he understood the political danger Antony posed, but Brutus refused because he thought it would make them “butchers.” Now the same divide appears again: Brutus still cares more about moral purity than political advantage, while Cassius thinks Brutus is being unfair and unrealistic.

Their quarrel also reflects the growing collapse of the conspiracy. The men who once united to save Rome are now suspicious and bitter toward one another. Shakespeare shows that Brutus’s honorable nature, which made him join the conspiracy for what he believed was the good of Rome, also makes him difficult as a political leader. His devotion to principle keeps putting him at odds with Cassius’s more calculating approach.