In Act 2, Scene 1, as Brutus paces in his garden, he comes to the realization that Caesar must die. He shares his thoughts with the audience through a soliloquy:
It must be by his death. And for my part
I know no personal cause to spurn at him,
But for the general. He would be crowned:
How that might change his nature, there’s the
Question.
It is the bright day that brings forth the adder,
And that craves wary walking. Crown him that,
And then I grant we put a sting in him
That at his will he may do danger with.
Th’ abuse of greatness is when it disjoins
Remorse from power. And, to speak truth of Caesar,
I have not known when his affections swayed
More than his reason.
As with many soliloquies in Shakespearean tragedy, Brutus's speech is an important source of dramatic irony. By thinking out loud, he informs the audience of his intentions to help kill Caesar while Caesar himself remains in denial about any threat to his life.
This soliloquy is also significant for what Brutus reveals about how the political class of Julius Caesar wields its power: the many speeches politicians make throughout the play will appeal sometimes to emotion, sometimes to logic and reason. But the best, most equitable leaders will appeal to both emotion and reason. To Brutus, Caesar seems beholden only to logic—he shows no remorse, and is not swayed by his "affections"—and is therefore quite dangerous: the "abuse of greatness" comes when one's emotion fails to hold one's ambition for power in check. One of Shakespeare's chief concerns in Julius Caesar is the role of morality in politics, and this is Brutus's perception of how to rule morally.
In Act 2, Scene 1, during Brutus's soliloquy, he ponders the threat that Caesar may pose to the Roman Republic if he seeks to become a monarch. Using a simile, he compares Caesar to a snake egg:
And therefore think him as a serpent’s egg,
Which, hatched, would, as his kind, grow
Mischievous,
And kill him in the shell.
By this simile, the time to strike is sooner rather than later—to kill Caesar now, while still “in the shell,” renders him harmless and mitigates any damage he might stand to inflict on Rome. This is one of two sequences in Julius Caesar in which Brutus describes Caesar as a snake, a symbol of malevolent trickery found throughout Shakespeare's plays.
A constant question in Julius Caesar is whether people have agency in the course of their own lives, or if fate predetermines their path. Brutus's observation that Caesar is as a snake still in its egg would imply that Caesar is guaranteed to become a tyrannical ruler if left alive, with no alternative: if a snake egg hatches, a snake will emerge. Rather than wait and see, Brutus convinces himself in this soliloquy that the only course of action is to preemptively assassinate Caesar.
In Act 3, Scene 1, the conspirators finally strike against Julius Caesar and assassinate him during a meeting of the Senate. As Caesar's body lies bleeding on the ground, Mark Antony delivers a tearful soliloquy for his fallen friend:
O pardon me, thou bleeding piece of earth,
That I am meek and gentle with these butchers.
Thou art the ruins of the noblest man
That ever lived in the tide of times.
Woe to the hand that shed this costly blood!
Over thy wounds now do I prophesy
(Which like dumb mouths do ope their ruby lips
To beg the voice and utterance of my tongue)
A curse shall light upon the limbs of men;
Domestic fury and fierce civil strife
Shall cumber all the parts of Italy….
Antony’s soliloquy is an apology to his old friend for his readiness to make amends with his murderers. Antony displays his true self as a many-faced politician willing to appeal to anyone and everyone—he will show loyalty to Caesar's murderers even as he weeps over Caesar's body. In revealing the depth of his admiration for and fealty to Caesar, however, Antony also sets up the audience to understand the irony of his withering speech against Brutus in Act 3, Scene 2.
In Act 3, Scene 1, when Caesar refuses to hear the case of the banished Publius Cimber, he asserts his steadfast position with an arrogant flourish of simile:
But I am constant as the Northern Star,
Of whose true fixed and resting quality
There is no fellow in the firmament.
The skies are painted with unnumbered sparks;
They are all fire, and every one doth shine.
But there’s one in all doth hold his place.
So in the world: ‘tis furnished well with men,
And men are flesh and blood, and apprehensive.
Yet in the number I do know but one
That unassailable holds on his rank,
Unshaked of motion; and that I am he…
Caesar compares himself to the North Star—one fixed celestial body, unwavering even as the heavens swirl around him. In this constancy, Caesar believes he is “unassailable.” His speech is rife with dramatic irony, as the audience is by now well aware of the murderous plot against him and have witnessed on numerous occasions Caesar’s refusal to acknowledge the many signs (supernatural or otherwise) of his coming assassination.
This speech embodies the very thing that Caesar's enemies purport to fear—a constant, unwavering Caesar with the absolute power of a monarch. In asserting his power so forcefully, Caesar unwittingly validates Cassius's criticism and Brutus's fears. Sure enough, just a few lines after his speech concludes, the senators will assassinate him. Shakespeare presents unchecked bravado as a weakness rather than a strength in Julius Caesar, and this sequence shows that even absolute self-certainty can only get one so far.