The Houyhnhnms resumed their ancient and only debate in their grand assembly pertaining to the future of the Yahoos, and as they had not always lived in that country but had grown to be an offense, it was discussed how to dispose of them for good; and since Gulliver had revealed to his master how horses are castrated in their youth in England, it was suggested that this practice would in time cause the natural end of the Yahoos.
Gulliver reminds the reader how perfect life is on the island with Houyhnhnms: he enjoys good health, tranquility of mind, void of fear or insecurity, no folly from enemy, no damage from pride, vanity, and the like; and it is his Honor who brings to Gulliver’s attention all of the evils and stupidities of the Yahoos in England - that mankind is a contemptible and dismal creature. Not only is Gulliver sure that his family and friends are Yahoos, he is beginning to replicate the manners of a horse. Unfortunately, all good things come to an end, and his master reveals to him that the grand assembly agreed that it was not right to keep a Yahoo since it is against nature to believe one could find pleasure in such a creature; therefore they conclude that Gulliver must return to his own country.
Gulliver constructs a vessel to set out to sea and arrives on an island where an arrow from the natives injures him, and while he is able to get away, he finally resolves to return to them rather then live in England. However, men from Holland aboard a passing ship recover him, and while he finds it conscientiously difficult to tolerate them, the captain is quite generous and kind towards him. When Gulliver finally returns to England and is reunited with his wife and family, "the sight of them fills him with hatred, disgust, and contempt," including "shame, confusion, and horror."
The author states that the history of his travels are an intent to inform the reader, for the public good, and to instruct mankind, especially with his extended stay among the consummate Houyhnhnms. Gulliver rejects proposals for conquering nations founded by Englishmen and instead is of the opinion that it would benefit them more so if the Houyhnhnms were able to train and teach the English in those good virtues. Eventually, Gulliver is able to eat at the same table with his wife, and he is resolved to train up his own family in those same good virtues “that he may find them docible animals.”