I thought he was a sort of primitive savage, but he was something absolutely modern and up-to-date that only this ghastly age could produce. A tiny bit of a man pretending he was the whole.
Julia describes Rex Mottram in this way in Book 2, Chapter 2, speaking in retrospect about why her relationship with Rex ultimately fails. This chapter covers in broad brushstrokes Julia and Rex’s courtship, when Rex convinces Julia to abandon Catholicism for the sake of their marriage, which establishes the emotional and spiritual context for Julia’s behavior throughout Book 3. As Rex attempts to overcome any objections to their marriage, it becomes abundantly clear that he cannot approach things with any sort of depth. He initially wants to convert to Catholicism in order to have a larger wedding, a shallow and materialistic reason. When attending conversion classes, Rex parrots what he believes the priests want him to say instead of seriously considering the significance of what the priests mean. His inability to understand that conversion is a responsibility, not an aesthetic, bodes ill for his taking marriage seriously. When Julia says that he’s only “pretending” to be whole, she refers to his lack of substance, his desire to simply do things for their image without thought of their significance. Julia feels she has given up her religion for someone barely human.
This description of Rex also furthers the theme of the flimsiness of modernity. Throughout Brideshead Revisited, Charles describes modern London society as obsessed with fads instead of tradition, rejecting what is built to last for what is convenient. Rex, emblematic of this modernity, demonstrates that part of its weakness is that it rewards falsehood. As a Canadian immigrant, Rex has had to establish himself in London society by the sheer force of his own personality. The very aspects of Rex’s personality that help him navigate modern society with ease—his ability to ingratiate himself to others, his pragmatism, and his desire for efficiency—are signs of his lack of substance as a person. The word “pretend” here is instructive because it emphasizes the way Rex tends to ingratiate himself to others, by lying and pretending to get the result he wants.