The notion of tacit knowledge has been widely and diversely adopted in the knowledge management literature. It is used to cover knowledge which hasn’t yet been articulated as well as knowledge which various authors argue cannot ever be articulated. This paper seeks to review these differences and proposes a conceptual means of understanding the issues associated with tacit knowledge. It draws on the work of Collins and Kusch to introduce notions of polimorphic and mimeomorphic actions before raising implications for the practice of knowledge management.