“A Case of Identity” is framed around a conversation between Holmes and Watson about the bizarreness of everyday life, its impenetrable curiosity, and the supremacy of reason as a key to navigating the world: “Life is infinitely stranger than anything which the mind of man could invent,” says Holmes (225). This statement about life’s strangeness operates as a springboard. It sets up the genre of the story readers are about to embark upon, as this case of disguises and typewritten love letters and false trips to France is definitely a strange one.

However, the statement also announces Holmes’s complexity, in terms of not only temperament but intellectual disposition. Though he largely embodies rationalism, his assertion about the strangeness of life—that its mystery extends the grasp or invention of the mind—undermines that rationalism. Moreover, just as he blends the seemingly contradictory elements of mystery and rationalism, he unites two other opposite realities: inductive and deductive reasoning. While famous for deduction, Holmes more often uses induction. In other words, instead of beginning with hypotheses and testing them against observation, he often begins with observation and arrives at conclusions.

Holmes’s remark about strangeness establishes the very premise of inductive logic: Induction, unlike deduction, begins not with hypothesis but with observation.