William Kirby and William Spence's Introduction to Entomology is generally recognized as one of the founding texts of entomological science in English. This essay examines the ideological allegiances of the coauthors of the Introduction. In particular, it analyzes the ideological implications of their divergent opinions on animal instinct. Different vocational pursuits shaped each man's natural history. Spence, a political economist, pursued fact-based science that was shorn of references to religion. Kirby, a Tory High Churchman, placed revelation at the very heart of his natural history. His strong commitment to partisan sectarianism cautions against reference to a homogeneous "natural theology" that was an agent of mediation. Fissures in the "common intellectual context" reached beyond the clash between natural theologians and radical anatomists to render the intellectual edifice of natural theology structurally less sound for the future.