Who convinces Brutus to join conspiracy in The Tragedy of Julius Caesar?
At the opening of Shakespeare's Julius Caesar, Caesar enters Rome in triumph and glory from his victory over Pompey's sons, and he is now the most powerful person in Rome. Caius Cassius, a Roman senator and one of Caesar's generals, is jealous of Caesar and has aspirations to lead Rome himself. Cassius decides that Caesar must be assassinated and organizes a conspiracy against him amongst his fellow senators.
Cassius knows that he's not well liked among the people and that he doesn't have a particularly good reputation, so he decides to enlist his brother-in-law, Marcus Brutus, in the conspiracy. Brutus is well known, well liked, and honorable, and he's known to be a loyal friend to Caesar. Brutus will lend legitimacy to the conspiracy.
Unbeknownst to Cassius, though, Brutus already has concerns about Caesar's growing power and his immense popularity, which he expresses to Cassius when he hears a shout from the people praising Caesar.
BRUTUS: What means this shouting? I do fear the people
Choose Caesar for their king. [1.2.84–85]
Cassius takes this as his opening.
CASSIUS: Ay, do you fear it?
Then must I think you would not have it so. [1.2.86–87]
In order to plant doubts in Brutus's mind about Caesar's power and ability to rule Rome, Cassius tells Brutus a story about Cassius himself having to save a weak and frightened Caesar from drowning. He also tells him about a time that Caesar had a fever and cried out, "Give me some drink, Titinius," like a sick girl.
Brutus is starting to come around to Cassius's way of thinking, but Brutus is extremely reluctant to assassinate Caesar, his friend and benefactor. Cassius wants to make sure that Brutus joins the conspiracy, so Cassius plans to write some letters against Caesar and have them secretly delivered to Brutus's home.
CASSIUS: I will this night,
In several hands, in at his windows throw,
As if they came from several citizens,
Writings, all tending to the great opinion
That Rome holds of his name, wherein obscurely
Caesar's ambition shall be glanced at. [1.2.318–323]
Cassius needn't have gone to all that trouble to deceive Brutus. Brutus decides for himself at the beginning of act 2, scene 1, that Caesar must be assassinated.
BRUTUS: It must be by his death . . .
And therefore think him as a serpent's egg
Which hatch'd would as his kind grow mischievous,
And kill him in the shell. [2.1.10, 32–34]
After Brutus has decided that Caesar must be assassinated, he receives another one of Cassius's deceptive letters. Even though Brutus has made up his mind about joining the conspiracy, this letter, and the ones he's received previously, convinces him that he's made the right decision.
BRUTUS: Such instigations have been often dropp'd
Where I have took them up. . . .
O Rome, I make thee promise,
If the redress will follow, thou receivest
Thy full petition at the hand of Brutus! [2.1.49–50, 56–58]
Cassius and the other co-conspirators have gone to meet Brutus at his home, intending to convince him to join the conspiracy, but they're surprised and pleased to learn that Brutus has already decided to join them. In fact, Brutus takes charge of the conspiracy himself!
BRUTUS: Give me your hands all over, one by one. [2.1.117]
After advising the conspirators that Marc Antony should not be killed along with Caesar and discussing how to make sure that Caesar goes to the Senate later that day (the Ides of March!) so that they can kill him, he sends them off to prepare for the day to come.
BRUTUS: Good gentlemen, look fresh and merrily;
Let not our looks put on our purposes,
But bear it as our Roman actors do,
With untired spirits and formal constancy.
And so, good morrow to you every one. [2.1.234–238]
The rest, as they say, is history.
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Cassius is the main conspirator who convinces Brutus to join the conspiracy, even though Brutus must come to the realization that while he loves Caesar, he loves his country (Rome) more before he agrees to become part of the plot to end the life of his leader.
Cassius uses an array of rhetoric, including a tale in which Caesar and he are swimming across the river, and while he makes it fine, he has to go back and rescue Caesar who isn't strong enough to fight against the current and bear the weight of his own armor. Cassius claims that Caesar is too weak, and his envy/jealousy shines through in his examples. However, Brutus eventually weighs the pros and cons, and decides that Caesar truly is a danger to the system of government and way of life that his country enjoys currently.
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