J. Swift on communication and veracity - why lie?

This is excerpted from Gulliver's Travels, Part IV, Chapter 4. Gulliver finds himself (a curious application of the active voice:-) in a land where the top of the food chain is occupied by the Equine species. Houyhnhnms are horses, and bipeds are Yahoos, with many Cretan characteristics.

MY MASTER heard me with great Appearances of Uneasiness in his Countenance, because Doubting, or not believing, are so little known in this Country, that the Inhabitants cannot tell how to behave themselves under such Circumstances. And I remember in frequent Discourses with my Master concerning the Nature of Manhood, in other Parts of the World, having occasion to talk of Lying, and false Representation, it was with much Difficulty that he comprehended what I meant, although he had otherwise a most acute Judgment. For he argued thus: That the Use of Speech was to make us understand one another, and to receive Information of Facts; now if anyone said the Thing which was not, these Ends were Defeated; because I cannot properly be said to understand him; and I am so far from receiving Information, that he leaves me worse than in Ignorance, for I am led to believe a Thing Black when it is White, and Short when it is Long. And these were all the Notions he had concerning that Faculty of Lying, so perfectly well understood among human Creatures.