Cassius hates Caesar for both personal and political reasons. Personally, Cassius resents the fact that he owes his life to Caesar’s mercy, as Caesar spared him from execution. Previously, Cassius was fact of Pompey’s, Caesar’s rival, faction. After Pompey’s defeat, Cassius and several others were pardoned. Politically, Cassius is jealous that Caesar has gained so much power, and is on the threshold of becoming Emperor of Rome.
To combat this, Cassius along with others formed the the conspiracy. In order to add value and credibility to the conspiracy, Cassius does his best to convince Brutus to join them. He uses a roundabout approach to convince Brutus. Cassius knows that Brutus strongly opposes the ascension of a single dictator, in this case, Caesar, one of Brutus’ good friends. He uses this to suit his purposes. He says “Well, Brutus, thou art noble; yet I see thy honorable metal may be wrought from that it is disposed.” Since Brutus was already thinking about going against Caesar, it takes little effort on Cassius’ part to convince him. However, to ensure Brutus’ cooperation, Cassius plants fake letters to trick him into believing that the citizens are also in favor of removing Caesar.
By joining the conspiracy, Brutus not only added credibility, but also added the solid framework of the conspiracy. Indeed, it appears that Brutus is the first one who explicitly states that Caesar needs to die. In his monologue, he says, “And therefore think him as a serpent’s egg- which, hatched, would as his kind grow mischievous, and kill him in the shell.” Presumably, it is also Brutus who came up with the assassination plan.
After Brutus joins