The Iliad: Situational Irony 1 key example

The plan to have Patroclus fight on behalf of Achilles is already initiated in Book 11, when Nestor suggests that Patroclus join the battle wearing Achilles's armor. Nestor hopes that the Trojans will take Patroclus for Achilles, hold off from attack, and give Achaea's "exhausted" forces a "second wind." The plan results in an ironic outcome. While it has the intended effect of turning the tide of the war in favor of the Achaeans, it's not for the reason Nestor or anyone else has in mind. When Achilles later decides to rejoin the war in order to avenge Patroclus's death, Patroclus's participation in the becomes marked by situational irony.

At the beginning of Book 16, Patroclus returns to Achilles and begs to let him fight on his behalf. After quoting Patroclus's speech, Homer comments that the character is "condemned to beg for his own death and brutal doom." By foreshadowing Patroclus's death in such straightforward terms, Homer creates dramatic irony. This irony is strengthened when Achilles reaffirms that he won't relax his anger until "the cries and carnage" reaches his own ships. The reader begins to expect that the cries and carnage will reach Achilles's ships when Patroclus dies. Again and again, he instructs Patroclus to "come back" before he reaches Troy—again and again, Homer reinforces the reader's expectation that he won't return alive. 

Not only is there dramatic irony between the reader and characters, but also between the characters themselves. As in many other instances, the immortals know more than the mortals—after all, the immortals play an important role in determining the mortals' fates. The lead-up to Patroclus's death is a good example of this. Later in Book 16, when Achilles prays to Zeus to fill Patroclus's heart with courage and let him come back unharmed, Homer shares that Zeus grants the first prayer, but denies the second one. Achilles knows what will bring him back into war, and that his return to war will result in his own death, but he's in the dark about Patroclus's role in all of it. In a way, the mortals are constant subjects of dramatic irony. Even when they know a piece of their fate, they never have access to Zeus's full picture.