Antony's famous lines in the last act of Julius Caesar declare that Brutus was the "noblest Roman of them all./ All the conspirators save only he (Brutus)/ Did that they did in envy of great Caesar." While Antony's last lines may be memorable, are they accurate? Is everyone else truly acting out of jealousy?
This is an excellent question. It is impossible to say what motivated all of the conspirators because Shakespeare provides little or no information about most of them. It might be fairly safe to guess that many of the conspirators were acting out of fear of Caesar, fear of what he might do to them personally or to their friends and relatives, if he obtained the absolute power he was obviously seeking. Cassius seems to be envious of Caesar, but he is also afraid of him because he knows Caesar, quite wisely, dislikes and distrusts him. What Cassius says to himself in a soliloquy after parting with Brutus in Act 1, Scene 2 reveals his true feelings better than anything he said to Brutus.
Well, Brutus, thou art noble; yet, I see,
Thy honourable metal may be wrought
From that it is disposed: therefore it is meet
That noble minds keep ever with their likes;
For who so firm that cannot be seduced?
Caesar doth bear me hard; but he loves Brutus:
If I were Brutus now and he were Cassius,
He should not humour me.
Maybe Cassius envies Brutus as much as he envies Caesar. What Caesar says about him to Antony earlier is undoubtedly accurate.
Would he were fatter! But I fear him not:
Yet if my name were liable to fear,
I do not know the man I should avoid
So soon as that spare Cassius. He reads much;
He is a great observer and he looks
Quite through the deeds of men: he loves no plays,
As thou dost, Antony; he hears no music;
Seldom he smiles, and smiles in such a sort
As if he mock'd himself and scorn'd his spirit
That could be moved to smile at any thing.
Such men as he be never at heart's ease
Whiles they behold a greater than themselves,
And therefore are they very dangerous.
So Cassius is envious of Caesar and afraid of him, although he would be quite content to see Caesar crowned king if it would do him any good personally. He is thoroughly selfish and mean-spirited. He is the chief instigator of the assassination plot, and most of the other assassins are motivated by whatever Cassius has told them. This includes Casca, whom Cassius invited to supper and then to dinner so that he could work on him the way he was so strenuously working on Brutus.
Antony is devoted to Caesar and does not see the potential tyranny that we ourselves can see in the man. Antony is not a reliable judge of the motives of the assassins. He attributes a single motive to all of them except Brutus. There were plenty of men, including Flavius and Marullus, who regarded Caesar as a potential tyrant--a sort of Huey Long or Adolf Hitler or Josef Stalin. They did not especially envy Caesar so much as they feared him. Caesar must have had more supporters than Antony among the aristocracy, but he seems to be trying to use the plebians to gain his ends. A lot of the patricians hate and fear Caesar because they do not want to see the republic destroyed. Brutus becomes the leader of the conspiracy just because it was his ancestor who drove a former tyrant out of Rome and restored the republic.
Brutus is undoubtedly the noblest Roman of them all, but he is not the only patriot among the conspirators. They are following Brutus because he represents them and what they believe in. Cassius may be exceptional in being as selfish and envious as he obviously is. The others' feelings and motives are probably mixtures of patriotism, selfishness, fear, and envy. Antony is oversimplifying out of his love for Caesar and his bitter hatred for the men who murdered him.