Purpose: This paper aims to clarify that the link between Michael Polanyi's tacit knowledge theory and the field of knowledge management research does not withstand in-depth analysis. Second, the paper suggests a way to emerge from the ambiguity that unavoidably results from using the tacit knowledge concept in knowledge management studies. Design/methodology/approach: The paper begins with an analysis of the tacit knowledge theories developed by Polanyi, by cognitive psychologists and by knowledge management scholars. It goes on to formulate a new conceptual framework of tacit knowledge. Findings: This proposal consists in assuming that the terms "unconscious" and "tacit" are not interchangeable and, consequently, redefining the epistemological profile of knowledge management theory so as to acknowledge the existence of two planes of analysis. One is occupied by the process through which individuals gain knowledge, or the knowing process, which may be unconscious or conscious. The other contains the dichotomy between tacit knowledge and explicit knowledge, where the two terms indicate two alternative states that only consciously developed knowledge can adopt. Research limitations/implications: The paper provides support for the two-planes idea by referring to contributions from various disciplines, and particularly from cognitive psychology studies concerned with unconscious knowledge; a more thorough and extensive review would be needed, however, to fully demonstrate the proposal. Originality/value: Distinguishing between two planes of analysis makes it possible to unveil the mystery of tacit knowledge.