Swift was a clergyman and did not agree with the optimistic view in the eighteenth century that human nature was essentially good. He believed that, .
human beings were not on this earth to be knowledgeable, happy, and powerful, but rather to be as morally virtuous as possible.10.
The new idea of man's rationality was threatening this insight. .
Swift defined the human species as not "a rational animal" but as merely "an animal capable of reason.
In Gulliver's third journey, Swift's satirizes the philosophical movements of rational thought. The Laputians are entirely preoccupied with contemplating deep concepts and ideas that never result in action:.
The Minds of these People are so taken up with intense Speculation, that they neither can speak, nor attend to the discourse of others.
However, Swift's main attack on man's rationality takes place in Gulliver's forth journey. There are two different creatures in the new world which Gulliver travels to, The Yahoos and the Houyhnhnms. The Yahoos have a physical resemblance to human beings, but their behaviour is animalistic. They are sexually promiscuous, physically strong, but also cowards. The Houynhnms are horses and have their own sophisticated language. They are also totally rational in their way of thinking. Both these creatures as we can see, have a resemblance to human beings. We can say they represent two different sides of human nature. So how does Swift use this created world to attack man's rationality? Gulliver's transformation in this world, can be seen as the main satirical target. Gulliver is revolted by the Yahoos, and does everything he can to adapt to the Houynhnms way of life. Swift is attacking the pride of contemporary Europeans, who thought of themselves as rational animals. But can we deny, that are behaviour often resembles the Yahoos, and that we are far to irrational creatures to live our lives like the Houynhnms? His mayor point is, that since we are only animals capable of reason, we should stop pretending to be rational animals.