The motif of reflections and mirrors in general underscores several important themes in the novel, including the Quest for Knowledge, Theory Versus Practice, and The Magical World Versus the Mundane World. When Jonathan Strange uses a basin of water to work his first spell, the reflection he sees marks his first step toward the pursuit of magical knowledge. When Mr. Norrell and Strange first meet, they become a pair after Strange takes a real book and causes it to switch places with its mirrored reflection. The two men even grow to become mirror opposites of each other, Strange with his reckless pursuit of practical magic and Norrell with his lack of practical knowledge and deep theoretical understanding.

Reflections also mark the physical boundary between the magical world and the mundane world, for when Norrell flees to Hurtfew to protect his library, he explains that any reflective surface is a potential opening through which Strange can attack him. The ubiquity of reflective surfaces shows that the presence of magic is inescapable in the ordinary world, and while Norrell sees its omnipresence as a threat, Strange sees it as a way of expanding his reach as a magician.