How does Swift use irony in Gulliver's Travels?

occurs when there is
some discrepancy between what we expect and what the reality is. We do not really expect
Gulliver to end up in locations where human beings are so very different, physically, than the
way we are or he is.  First, he arrives in Lilliput, where the humans are only about six inches
tall. Then he gets stranded on Brobdingnag, where he is dwarfed by the natives' giant size.
Ultimately, he travels to Houyhnhmland, where horses are civilized and run the society, and
humanlike creatures are called Yahoos. They are totally uncivilized and used like livestock by
the Houyhnhnms. We would certainly be unlikely to expect to see a society where the horses are
in charge and use people like we use horses.

Further, Swift employs irony in
Gulliver's third voyage to Lagado. There, he sees scholars and intellectuals working on such
experiments as trying to extract sunshine from a cucumber or reanimate a dead dog by placing a
bellows in his anus and pumping him full of air. We would hardly expect to see such absolutely
ridiculous experiments being conducted by people who are like the most highly educated, the most
intelligent among us.

In the end, Gulliver decides that the Houyhnhnms really
are the master race, agreeing with them about the dirtiness and stupidity of humans. When he
returns home, he cannot stand the smell of his wife and children, and he generally finds
everyone he once thought so wonderful absolutely disgusting. After Gulliver has spent so long
defending his home country, customs, and government to so many individuals, against so much
criticism, we would not expect him to turn on his countrymen and women the way he does. This,
too, is ironic.