Textualism is the notion that nature itself is in some sense literally a text, a self-contained product of definition like a deductive system or a machine. This is a persistent and largely unacknowledged background assumption inherited by science from the medieval concept of the Book of Nature. Textualism is a thema, in Gerald Holton’s sense. The view of the universe as a result of divine decree, or as a machine running on without the ongoing support of divine will, represented an extension of medieval interest in textual exegesis. In that light, the Book of Nature could best be studied in syntactic terms, specifically with mathematics as the most efficient way to express and interpret the syntax of the world. The idea of the world as text is closely related to that of the world as a divine artifact—indeed, as a machine. Texts, artifacts, and machines are made by design. They possess only the reality defined by their creators and users. Like other artifacts, including machines, a text is a finite, self-enclosed product of definition, containing no more than what was explicitly inscribed by its author along, with deductions implicit within that original specification. If nature is a text, then it should be as predictable as a machine and as searchable as other texts. It should subject to the methods of textual interpretation that were applied to Scripture. Historical time was identified with biblical narrative. The ability to search the text was conflated with the ability to search actual time, making prophecy plausible. Events are predictable in a deterministic system for similar reasons: it is a deductive system, a product of definition, like a text. Whether expressed in Scripture or in the physicist’s equation, the text—while open to interpretation—is determinate and searchable, in a way that nature itself is not.