"nothing is great or little otherwise than by Comparison"
The philosopher Swift has in mind was his friend George Berkeley (1685-1753) who developed a subjective theory of knowledge: one could learn only by sense perception (outside the area of religion) with such sense perception notoriously unreliable and incapable of demonstrating truth or reality. In his book, Essay Towards a New Theory of Vision,
Berkeley stressed the relativity of judgment. The book was published in 1709.