The proposal is made in Act 2, scene 1, when the conspirators to Caesar's assassination all meet at Brutus' house during the night. They have all agreed that Caesar should be prevented from becoming much too powerful for he would be a tyrant. Brutus believes that doing this would be for the sake of all Rome and his involvement is not borne out of selfish desire. On a suggestion that they make a pledge, Brutus refuses, stating that if they (the conspirators) do not feel bound enough by a noble ideal, then they should all forget about the plot and return to their beds.
After a discussion on why Cicero should not be included in the plot, since Brutus believes that he would 'not follow anything that other men begin', Decius Brutus asks the following:
Shall no man else be touch'd but only Caesar?
Decius, well urged: I think it is not meet,
Mark Antony, so well beloved of Caesar,
Should outlive Caesar: we shall find of him
A shrewd contriver; and, you know, his means,
If he improve them, may well stretch so far
As to annoy us all: which to prevent,
Let Antony and Caesar fall together.
It is clear that Cassius fears that Antony is an evil schemer and plotter and he feels that if Antony should by his talents extend his influence, he may become powerful enough to cause them all problems. To prevent this from happening, it is best that Casar and Antony are slain together. Brutus responds to this suggestion by saying:
Our course will seem too bloody, Caius Cassius,
To cut the head off and then hack the limbs,
Like wrath in death and envy afterwards;
For Antony is but a limb of Caesar:
Let us be sacrificers, but not butchers, Caius.
We all stand up against the spirit of Caesar;
And in the spirit of men there is no blood:
O, that we then could come by Caesar's spirit,
And not dismember Caesar!
... We shall be call'd purgers, not murderers.
And for Mark Antony, think not of him;
For he can do no more than Caesar's arm
When Caesar's head is off.
Brutus is of the opinion that Killing Antony would make them seem too bloodthirsty. He uses a metaphor, comparing Ceasar to an important body or tree of which Antony is but an extension (a limb) and cutting of the limb after killing its source, would seem to be vengeful and envious. He believes that they should be seen as making a sacrifice, not as butchers. Their target is Caesar's spirit, not his body. Brutus further insists that they should be seen as ones who have cleansed Rome of an evil affliction, not as murderers.
He asks that Mark Antony should not be considered a threat, he extends the metaphor, stating that Antony would be just as useful as an arm once the head has been cut off, meaning that Antony would be powerless after Caesar has been killed.
When Cassius expresses doubt, saying that he fears Antony because he had a natural affinity for Caesar, Brutus assures him that:
... all that he can do
Is to himself, take thought and die for Caesar:
And that were much he should; for he is given
To sports, to wildness and much company.
Brutus does not see Antony as a threat at all. He believes that once Caesar has been assassinated, Antony would become introspective and grieve for Caesar. He would be overwhelmed with sorrow and despair and die. Furthermore, if that should not happen, Antony would have many other distractions, for he enjoys sports, doing wild things and keeping company.
The above discussion between Brutus and Cassius indicates a clear contrast between the two men. Cassius seems to have a more acute sense and understanding of the human condition, whilst Brutus appears naïve and uninformed. It is this naivety and trust that Brutus would regret later, when Antony instigates the Roman populace to rise up against him and his fellow conspirators.