In Chapter 2 of The Sword and the Stone, White uses the reader's expectations for dramatic, regal quests to create a moment of situational irony. After trying to do some amateur falconry with Kay, Wart becomes separated and gets lost in the woods. Soon, arrows fly at him from unidentified assailants. He ducks for cover, fearing for his life. Then, he sees "the most beautiful thing he had ever seen in his short life." The reader, familiar with the story trope of deus ex machina, in which a hero arrives just in time to save the helpless, expects that Wart is safe at last. The beech trees shine in the moonlight, and Wart sees a knight before him:
He was mounted on an enormous white horse who stood as rapt as his master, and he carried in his right hand, with its butt mounted on the stirrup, a high, smooth, jousting lance, which stood up among the tree stumps, higher and higher, till it was outlined against the velvet sky. All was moonlit, all silver, all too beautiful to describe.
The imagery that makes the knight seem so beautiful is simple but effective. A long, confident sentence describes the knight's grand posture and appearance, its syntax following Wart's eyes as he surveys the mounted fighter. There is a sense of quiet, resting power in the scene. To the reader, this knight is as beautiful and awe-inspiring as it is to Wart. The reader has gotten exactly what they expected from this deus ex machina.
Then, the knight (who the reader eventually learns is King Pellinore) turns out to look like a stereotypical nerd from the fifties. This image is complete with "horn-rimmed spectacles, fogged by the inside of his helmet" and an overwhelming clumsiness. This archetype was used often as the butt of jokes in popular media when White was writing the novel. (The character of the nerd, then, had none of the redeeming qualities and cultural affinity that it gained in the 21st century.) So the expectations of this knight as a capable, chivalrous guardian are subverted—particularly by using the rich imagery of the description of the knight.
If a reader were to open The Once and Future King and not know what it was about, the character of Wart in The Sword and the Stone might be rather confusing. If that reader were to have accidentally skipped the first page in the novel, they would have no idea whatsoever who Wart is or why they should care about this wayward boy from medieval England. Only offhand, on the first page, does White give a quick sense of who Wart is: "The Wart was called the Wart because it more or less rhymed with Art, which was short for his real name." This is the only indication whatsoever, in the early part of the novel, that Wart is King Arthur. Without it, the reader might think this is just a random boy.
So it is quite jarring when, in Chapter 14, seemingly out of nowhere, White foreshadows with unbothered certainty who the Wart will grow up to be:
In other parts of Gramarye, of course, there did exist wicked and despotic masters––feudal gangsters whom it was to be King Arthur's destiny to chasten––but the evil was in the bad people who abused it, not in the feudal system.
This is the first instance of the phrase "King Arthur" in the text. This is such an explicit and undramatic bit of foreshadowing that it catches the reader off guard. It is, indeed, foreshadowing, as White uses one of the problems of an earlier point in the narrative (the moral status of feudalism) to describe a later point in the narrative (Arthur's Round Table maintaining peace in the land).
This unusual foreshadowing has particular effects. It confirms the total omniscience of the narrator, that it is entirely aware of all parts of Arthur's life at all times. This foreshadowing also suggests that the concepts of equality and justice exemplified in Arthur's Round Table were, perhaps, on his mind since his childhood.
It is, also, simply a funny subversion of expectations from White. The author made a bold decision by using one of the most famous characters in English literature, King Arthur, but referring to him with a false name for the first hundred pages of his novel. The reader might expect a grand reveal or tortuous quest to learn his real identity. Instead, White drops the name "King Arthur" in an innocuous bit of foreshadowing in the middle of Wart's narrative. This is one of the many ways that White manipulates a storybook structure to ironic effect.
As Queen Morgause is making her potion out of a black cat in Chapter 1 of The Queen of Air and Darkness, White uses situational irony to describe the situation:
The Queen knew that every pure black cat had a certain bone in it, which, if it were held in the mouth after boiling the cat alive, was able to make you invisible. But nobody knew precisely, even in those days, which the bone was. This was why the magic had to be done in front of a mirror, so that the right one could be found by practice.
One would think this gross, absurd situation would have some level of rigor and knowledge to it. White's version of witchcraft and magic in the novel usually has a distinct specificity. This witch, the reader thinks, ought to at least know this "easy and well known charm." But, in an ironic turn, she doesn't know this, and neither does anyone else. This particular instance of irony relies on the reader having a post-Enlightenment, post–Scientific Revolution mindset. In other words, such a reader believes, like many in the modern era, that experts ought to know which bones are which, relying on rigorous scientific methods. The situational irony in this passage works only with this modern-day mindset in the reader.
Note, also, that this cat potion was "an easy and well known charm" that "was an excuse for lingering with the mirror," and yet the queen still struggles with it. This ironic moment also works as characterization for the queen, suggesting that she would like an excuse for lingering in the mirror.
In Chapter 7 of The Candle in the Wind, Lancelot and Guinevere are under siege by what seems to be many knights, hearing "many more voices" and "many joints of harness." After the lovers share a moment, Lancelot prepares for the conflict but, in a moment of simple situational irony, is underwhelmed:
He put his shoulder against the leaping door and softly pushed the beam back, into the wall. Then, still holding the door shut with his shoulder—the people on the other side had desisted from their hewing, feeling that something was about to happen—he settled his right foot firmly on the ground about two feet from the door jamb, and let the door swing open. It stopped with a jerk at his foot, leaving a narrow opening so that it was more ajar than open, and a single knight in full armor blundered through the gap with the obedience of a puppet on strings.
This is a rather simple but funny instance of situational irony. The leader is led to believe that there is a horde of scary knights just outside the door. White builds the suspense and tension as Lancelot, nearly naked and weaponless, scrambles to defend himself. Then, just as the moment of conflict arrives, Lancelot opens the door and one knight "blunder[s] through the gap." This sort of joke—the blundering knight—is used often throughout the book. It is a compelling irony, as the book also puts a special focus on chivalry and the training involved in knighthood. Even in a scene that is generally quite serious, White, as he does so often, uses physical, slapstick humor. This is perhaps the fundamental joke of the novel: we expect knights to always be coordinated, strong, and chivalrous, when in reality they are just people—and people often blunder.