Shakespeare's Julius Caesar is so very relevant today, especially when the reader examines the characters as representative of personality types. Brutus is, of course, the ideologue and his counterpoint, Cassius, is the practical-minded man; however, in order to solicit the aid of Brutus in the conspiracy, Cassius knows he must feign the ideologue because rarely does an ideologue stoop to doing what is practical or exigent.
Therefore, even though he has been swayed by forged letters thrown over his orchard wall, even though his wife has had premonitions in her dreams the night before, and even though Brutus has little or no empirical proof that Caesar does want to become emperor, in his mind previously praised by Cassius, he wonders if Caesar will continue to be just and honorable (as he has been) if he should be given the power of an emperor. Finally, then, based solely upon his personal perceptions and ideology, which have been clouded by Cassius's machinations, Brutus decides--objectively, he believes--that Caesar must be killed on theory. He feels Caesar might become tyrannical:
...think of him as a serpent's egg
Which hatched, would as his kind grow mischievous. (2.1.32-33)
In his idealism Brutus also fails to comprehend the warnings of Cassius about Marc Antony and his practical advice to slay him. Nor does he listen to Cassius's most practical advice that Antony can do irreparable damage to them and to Rome and he should be immediately killed. Instead, the idealistic Brutus trusts Antony to be honorable, too. Of course, Brutus makes a grievous mistake and Antony in his personal revenge, initiates a civil war, the worst condition which a country can suffer.
Antony, who understands people, creates the seeds of doubt about Brutus in the minds of the pleblians, when previously, Brutus has eloquently and idealistically delivered his message that he killed Caesar because he loved Rome more. Earlier he has said,
...and then is death a benefit
So are we Caesar's friends, that have abridged
His time of fearing death. (3.1.)
And, it is this message that he delivers to the Roman citizens, asking the rhetorical question,
Had you rather that Caesar were living, and die all slaves, than that Caesar were dead, to live all free men? (3.1.)
Thus, Brutus killed Caesar on theory, because of his idealism. This is a fragile argument if the character of Brutus as anything less than noble can be established. Indeed, defamation is exactly what Marc Antony has accomplished as he brings forth actual documents and practical decisions of Caesar into his argument. He creates questions about the integrity of the assassins. "For Brutus is an honorable man; so are they all honorable men."
Truly, "Between the Idea and the Reality....lies the Shadow" as T. S. Eliot wrote. Brutus, the idealist brings civil war onto the Romans and shatters the State. Idealism rarely works because it is never practical.