Purpose: Review role of Fisher’s Separation Theorem in its historical context. Originality: Investigate a shift in pattern of economic thinking on determinants of the rate of interest. Key Literature/Theoretical Perspective: The evaluation is conducted against the backdrop of a conceptually intriguing series of events, spanning and surrounding publication of Fisher’s works The Rate of Interest (1907) and The Theory of Interest (1930). Approach: Historiography, or Historical Method - and more precisely, Historical Reconstruction [McCloskey (1976), Tuchman (1994)]. Analytical techniques applied to published and archival materials include Contextual Analysis [Marcuzzo (2008), Stigler (1965)] and the impact of language – especially myth, plot-structure, cultural endowment [Dolfsma & Welch (2009)], and metaphor [Klamer & Leonard (1994)]. Findings: Arguably, study of archival materials can provide insights into motivations and intentions that underpinned theory conception and development; much like adjusting image resolution - to bring into focus an object - where at first, only contours are visible [Marton & Booth (1997)]. Research Limitations/Implications: The data is text. Findings are interpretive truths. Practical and Social implications: Knowledge about episodes in the history of economic thought literature - especially instances where a series of events shifts a pattern of thinking - is essential for studying the mechanics of conceptual novelty. Thereby, illuminating patterns that we may anticipate in past, present, and future economic thought.