Gulliver proceeds to study the Houyhnhnm’s language under the tutelage of the master horse, a kind and patient teacher who marvels at Gulliver’s un-Yahoo-like capacity for learning and reason. He asks about Gulliver’s origin but does not believe Gulliver’s account, since he can’t imagine Yahoos being in charge of any country. He suggests Gulliver’s story is “the thing which was not,” since the Houyhnhnm language has no word for “lie.”
From the Houyhnhnms’ perspective, it is remarkable that humans could learn and reason since they attribute those abilities only to horses. Because he lacks the worldly knowledge Gulliver possesses, the master horse has trouble conceiving of other societies. The fact that their language lacks even the word for ‘lie’ proves just how honest Houyhnhnm society must be.
The Houyhnhnms continue to think that Gulliver’s clothes are a part of his body and Gulliver takes care to undress only in their absence so as to keep up the illusion and thereby distinguish himself from the Yahoos as much as possible. But one day, a servant disturbs Gulliver in his sleep and sees his naked body. The master horse asks Gulliver to explain himself and Gulliver undresses for his gentle admiring examination. He calls Gulliver a perfect Yahoo, though Gulliver says it bothers him to be called a Yahoo of any sort. He also asks the master horse to keep the truth about his clothes a secret, which the master horse consents to.
Again, Gulliver contradicts his professed devotion to complete truthfulness. The care Gulliver takes to keep up the Houyhnhnms’ illusions about his clothes isn’t strictly a lie but it is certainly an evasion of truth. By agreeing to keep the truth about Gulliver’s clothes a secret, the master horse sympathizes with his perspective, understanding Gulliver’s desire to distance himself from the Yahoos.
Once Gulliver gains enough fluency, he begins to tell the master horse about Europe, asking the master horse please not to be offended by the tale of his past. The master horse is still puzzled by the possibility that Yahoos would be capable of building ships or that any Houyhnhnms would allow them to be in charge of such a project. Gulliver explains that, where he comes from, Houyhnhnms are irrational beasts and Yahoos are the rational rulers. He tries to make the master horse understand by saying that he was just as astonished to find civilized Houyhnhnms here as the master horse would be to find civilized Yahoos in Europe.
The European and Houyhnhmn societies possess exactly opposite perspectives on the superiority of humans vs. animals. Gulliver uses his worldly knowledge (his experience of both European and Houyhnhmn society) to try and help the master horse understand the European perspective.