Adept at languages, Gulliver learns rather quickly to talk with the Houyhnhnms. They speak a strange language, he says, yet it is similar to High Dutch. Besides the Houyhnhnms teaching Gulliver, he teaches them. They have no books, so Gulliver shows them how to write. The Houyhnhnms are truly mystified by their visitor; he seems to be so much like a Yahoo, but he also seems to be a rational Yahoo — a combination which they believe to be impossible. Gulliver describes for the Houyhnhnms the mutiny that stranded him, and they are astonished by the notion of a "lie." Horses, they say, do not even have a word for the concept of lying. They explain further that besides Houyhnhnm meaning "horse," it is derived from a word meaning "perfection of nature." Gulliver's Houyhnhnm host is curious about Gulliver's modesty. After all, he reasons, why would anyone want to conceal what nature has made? When he is naked, however, Gulliver looks very much like a Yahoo, so Gulliver's host promises to keep his guest's clothing a secret.
Swift continues the theological implications he began with the dietary references in the first chapter. A Germanic scholar in the Renaissance had learnedly and earnestly proved that the language Adam and Eve spoke in paradise was High Dutch. Also, Charles V is supposed to have said that he would speak to his God in Spanish, his friend in English, his mistress in French, and his horse in German. The theory that Adam and Eve spoke German was familiar to Swift's audience. Milton had joked about it before Swift.
Swift has established the distinctions between Gulliver, the horses, and the Yahoos by using physical and concrete objects. He makes his point explicit by defining Houyhnhnm, which means "perfection of nature." This definition establishes an important distinction. The horses are uncorrupted by passion — either base or noble. They are devoid, for example, of charity. Also, they are not subject to temptation. Like Adam, they cannot understand the use of clothing. Swift never suggests that the Houyhnhnms stand for perfected human nature; on the contrary, they manifest innocent human nature. What they do — and what they say and think — is akin to human nature, but the character of the Houyhnhnms is far from Gulliver's. They are ignorant of many things which most people would consider venial. They cannot, for example, understand lying — or even the necessity for lying.
Swift thus establishes a range, or spectrum, of existence. The horses are literally innocent, having never (in theological terms) "fallen"; the Yahoos are super-sensual and depraved. The Houyhnhnms are ice-cold reason; the Yahoos are fiery sensuality. In between these extremes is Gulliver.
glimmerings of reason faint manifestations of rational thinking; here, meaning, that it might be possible for a Yahoo (Gulliver) to show some thinking ability.
prodigy an extraordinary happening; here, meaning that a "brute animal" (the Yahoo, Gulliver) could show possibilities of being a "rational creature."
pastern the part of the foot of a horse just above the hoof.