Gulliver stays home for five months, but he then leaves his pregnant wife to set sail again, this time as the captain of a ship called the Adventure. Many of his sailors die of illness, so he recruits more along the way. His crewmembers mutiny under the influence of these new sailors and become pirates. Gulliver is left on an unknown shore, after being confined to his cabin for several days. In the distance, he sees animals with long hair, goatlike beards, and sharp claws, which they use to climb trees. Gulliver decides that these animals are extremely ugly and sets forth to find settlers, but he encounters one of the animals on his way.
Gulliver takes out his sword and hits the animal with the flat side of it. The animal roars loudly, and a herd of others like it attack Gulliver by attempting to defecate on him. He hides, but then he sees them hurrying away. He emerges from his hiding place to see that the beasts have been scared away by a horse. The horse observes Gulliver carefully, and then it neighs in a complicated cadence. Another horse joins the first and the two seem to be involved in a discussion. Gulliver tries to leave, but one of the horses calls him back.
The horses appear to be so intelligent that Gulliver concludes that they are magicians who have transformed themselves into horses. He addresses them directly and asks to be taken to a house or village. The horses use the words “Yahoo” and “Houyhnhnm,” which Gulliver tries to pronounce.
Gulliver is led to a house, and he takes out gifts, expecting to meet people. He finds instead that there are more horses in the house, sitting down and engaged in various activities. He thinks that the house belongs to a person of great importance, and he wonders why they should have horses for servants. A horse looks Gulliver over and says the word “Yahoo.” Gulliver is led out to the courtyard, where a few of the ugly creatures Gulliver has seen are tied up. Gulliver is lined up and compared with one of the creatures, and Gulliver finds that the creature does look quite human. The horses test Gulliver by offering him various foods: hay, which he refuses, and flesh, which he finds repulsive but which the Yahoo devours. The horses determine that he likes milk and give him large amounts of it to drink.
Another horse comes to dine, and they all take great pleasure in teaching Gulliver to pronounce words in their language. They cannot determine what he might like to eat until Gulliver suggests that he could make bread from their oats. He is given a place to sleep with straw for the time being.
Gulliver endeavors to learn the horses’ language, and they are impressed by his intellect and curiosity. After three months, he can answer most of their questions and tries to explain that he comes from across the sea, but the horses, or Houyhnhnms, do not believe that such a thing is possible. They think that Gulliver is some kind of Yahoo, though superior to the rest of his species. He asks them to stop using that word to refer to him, and they consent.
Gulliver tries to explain that the Yahoos are the governing creatures where he comes from, and the Houyhnhnms ask how their horses are employed. Gulliver explains that they are used for traveling, racing, and drawing chariots, and the Houyhnhnms express disbelief that anything as weak as a Yahoo would dare to mount a horse that was so much stronger than it. Gulliver explains that the horses are trained from a young age to be tame and obedient. He describes the state of humanity in Europe and is asked to speak more specifically of his own country.
In the fourth voyage, Gulliver reaches a stage at which he no longer cares for humankind at all, though in this section we see only the beginnings of his transformation. After visiting countries in which he is too large, too small, and too down-to-earth, he finds himself in a country where he is neither rational nor moral enough, stuck in the limbo between the humane Houyhnhnms and the untamed, unruly Yahoos. In these chapters we see the rough outline of Houyhnhnm society, which Gulliver finds pleasant but still alien. In the next section, he attempts to become a part of this society.
In the meantime, we are treated to a description of the Houyhnhnms’ society. Swift plays a clever trick in the first two chapters, obscuring the true nature of the Houyhnhnms so that we follow Gulliver in his mistaken belief that the horses are magicians or the servants of a magician. Instead of telling us outright that the horses are intelligent, Swift allows us to discover this fact through Gulliver’s eyes. As a result, what looks strange to Gulliver also looks strange to us, and at some point in the description of the horses’ behavior, we realize that there is nothing more to these creatures than meets the eye. Instead of being tools of humans, the horses are revealed to be intelligent in their own right. In one stroke, they go from being a manifestation of humanity to something utterly nonhuman.
There are a number of differences between the first three voyages and the fourth. Three of these differences are particularly important because they signal changes in the overall satirical thrust of the novel: Gulliver finds himself not among fellow humans, however distorted in size or culture, but among a race of horses; instead of being happy to leave, he is eager to stay; and instead of seeing the world through his eyes, we are forced to step back and look at Gulliver himself as an important, though not always sympathetic, player in the drama.
In other ways, these chapters are similar to the initial chapters of the other voyages. Gulliver arrives in a strange land, becomes the guest or prisoner of the people who live there, learns their language, and slowly begins to learn about their culture and tell them about European culture. The major difference here is that the humans, or Yahoos, are not his hosts. Instead, they are vile creatures that get nothing but his contempt. In his descriptions of the Yahoos, Swift uses the technique of describing the familiar in unfamiliar terms. Only slowly does it dawn on us that the Yahoos are humans. As with the realization that the Houyhnhnms are intelligent in their own right, the sudden shock—which we experience along with Gulliver—of recognizing the Yahoos for what they are strengthens the impact of the description.