A Voyage to Lilliput: Mocking the Pompous
Gulliver's first voyage takes him to a land inhabited by people who are six inches tall. Lilliput and its rival kingdom of Blefuscu carry on as if their affairs were just as vital as those of European nations, and their nations just as capable, despite the fact that Gulliver could step on them all if he wished. As he records their society, court intrigues, religious disputes, and wars, it becomes clear that European politicians and aristocrats share much of the ridiculousness of the Lilliputians.
When Gulliver is finally forced to leave Lilliput, it is because of trumped-up charges of treason fabricated by court enemies. He spends a short time in Blefuscu, but because Lilliput threatens war over his presence there, he resolves to leave rather than cause further trouble.
When Gulliver journeys to a land of giants called Brobdingnag he experiences what it feels like to be a Lilliputian, as the giants are as much larger than him as he is larger than a Lilliputian. Gulliver's various brushes with death are humorous, but Swift also uses them to reinforce a major focus of this section: just as Lilliputian affairs are ridiculous because of their smallness, human pretensions are ridiculous as well.
Swift's second major target for satire appears when Gulliver tries to show the Brobdingnagian king the greatness of England; he succeeds only in showing its corruption. While English civilization is more complex and more technologically advanced than Brobdingnag, a large portion of the technology is devoted to war and destruction, and much of the complexity of law and government is an opportunity for massive corruption. Swift's satire has expanded in this section to cover the entire nation, and other European nations as well.
A Voyage to Laputa: Pretensions to Knowledge
Gulliver's third voyage, "to Laputa, Balnibarbi, Luggnagg, Glubbdubdrib, and Japan," is divided into four main sections (his visit to Japan at the end is brief). Each stop on Gulliver's trip mocks mankind's claims to knowledge and understanding in some way. Laputa, as an island of absent-minded thinkers floating in the air, gives a good picture of a people with impressive thoughts, but no good connection to reality.
When Gulliver leaves for the land of Balnibarbi below and enters the city of Lagado, the satire turns much harsher. Swift portrays there a group of men who, after spending some time in Laputa, attempted to apply their pet theories to the improvement of the country. But their ridiculous schemes have ruined it, because the theories took no account of reality. Still, most people follow their schemes, for they are after all new, modern, and scientific.
Glubbdubdrib is a land where magicians can temporarily bring the dead back to earth, allowing Gulliver to speak to various famous historical figures. He discovers, though, that much of the history he has read is inaccurate, through either the ignorance or bias of the historians. Swift also takes this opportunity to speak again of the frequent evil of even honored men such as religious leaders and aristocrats.
In Luggnagg, Gulliver himself comes in for mockery. Upon hearing of the existence of immortals in the land, he begins to imagine the greatness of their lives, and sketches out the life of learning and leadership he would live were he to be immortal. His host then informs him of one thing he has failed to understand -- the immortals do not have eternal youth -- a fact that overthrows his whole grand scheme.
A Voyage to the Country of the Houyhnhnms: Human Beastliness
Gulliver's final voyage is to a land of intelligent horses called Houyhnhnms, and beastly human-like creatures called Yahoos. In his depiction of the Yahoos, and the parallels he draws between their brutish behavior and that of humans, Swift expands his satire to the evils of the entire human race.
The perfectly rational and virtuous Houyhnhnms provide sharp contrast to this, leading Gulliver to eventually become so ashamed of his humanity he almost begins to act like a horse. Despite Gulliver's eventual elimination of some of his bad tendencies through imitation of the Houyhnhnms, he is eventually exiled on the argument that his combination of greater intelligence than Yahoos and lesser virtue than Houyhnhnms makes him dangerous.
The end of the story presents Gulliver's dilemma: he is now horrified by his fellow humans, yet his behavior in talking to horses and refusing to eat with his family is enough to make the reader wonder if he is insane. Gulliver's dilemma is also humanity's. Developing greater virtue can lead to hating humanity's corrupt nature, but trying to escape one's own human nature because of its corruption is insanity.
So throughout Gulliver's Travels, Swift repeatedly satirizes human corruption and inadequacy from a variety of angles. The four adventures progressively increase the scope and forcefulness of these attacks, leading to the thematic climax that ties off the plot.