This essay will consider the dispute between Charles Sanders Peirce and John Dewey on the nature and validity of the theory/practice distinction. Their dispute concerns whether a strong affirmation of this distinction enables scientific inquiry or disables it. Inherent in this issue are two related questions, namely whether tmth can be pursued for its own sake, and, as a subset of this question, whether there is an evidence proper to the consideration of pure possibilities. I will argue that there is a common ground between the logic of inquiry which Dewey is determined will have practical effect, and the logic of inquiry which Peirce is concemed will discover the truth promised by correct investigation. This compromise is found in the philosophy of Bemard Lonergan, whose critical realism includes an account of concrete judgement strikingly similar to that of John Dewey, but whose account of the normative stmcture of cognition, emanating from the individual's radical desire to know, also incorporates Peirce's emphasis on the pursuit of truth and on the validity of the scientist's consideration of pure logical possibilities. I will present these similarities, and will consider the stmcture of Einstein's 1905 paper, "On The Electrodynamics of Moving Bodies," as a case study which supports Lonergan's (and Peirce's) account of cognitional stmcture, but which poses problems for Dewe/s instrumentalism. The essay concludes that Lonergan offers a critical realism which successfully renounces the 'spectator' theory of knowledge without underestimating the importance of the normative element of understanding in the human desire to know.