We find out that Cassius feels slighted by Brutus' condemnation of Lucius Pella for taking bribes. Cassius is friendly with the man, and tried to beg forgiveness from Brutus, who refuses, in the name of justice. Brutus says that, because Caesar was killed in the name of justice, justice should be honored at all times, and he feels that Cassius has forgotten this. In addition, Brutus heard apparently false word from a messenger that Cassius had refused to sponsor the upcoming battle against Mark Antony and Octavius, and is angry. The two men explode in anger, which subsides as Cassius expresses anguish at being so alone, without the support of a formerly close friend. Brutus then backs down, and adds humor to the situation by implying that the argument was only due to Cassius' "womanly" humor. The two spar a bit more, before settling down and allowing that their tempers got the best of them.
As the argument subsides, an elder poet attempts to forcibly gain entrance to Brutus' tent. Officers force him back, but not before he tries to dispense advice to Brutus and Cassius. Brutus, especially, has no patience for the man, and wishes not to hear it. He gets so worked up about this, it turns out, because he has just heard that his wife, Portia, has killed herself by swallowing hot coals. She remained in the distraught state she was in the day Caesar was killed, and could not be consoled. Brutus first reports this news to Cassius, and then hears it again from the entering Titinius and Messala, who also bring news that Antony and Octavius have put over 100 Senators to death in the capitol to instill terror, and have arrived at Philippi. They then decide to advance to Philippi before battling Antony and Octavius, hoping to prevent those men from amassing greater numbers of loyal followers during a march from Philippi to Sardis. Brutus and Cassius, already having marched that distance while asking for money and food to support their cause, are no longer popular among the people. Brutus predicts:
"We, at the height, are ready to decline. There is a tide in the affairs of men, which, taken at the flood, leads on to fortune; omitted, all the voyage of their life is bound in shallows and miseries. On such a full sea are we now afloat, and we must take the current when it serves, or lose our ventures."Act IV, Scene III, Line 216
Afterwards, Brutus asks his servant Lucius for some music as the officers all drop off to sleep in Brutus' tent. As Lucius drops off to sleep, Brutus decides to read instead. While reading, he is distracted by a ghost who appears in the tent to speak to him. The others remain asleep while Caesar's ghost warns Brutus that they will meet again tomorrow at the plains of Philippi. Brutus is shaken, and wakes the others up to ask them if they have seen or heard anything amiss. They have not.
