The purpose of this paper is to discuss the uncertainty concept through a reconstitution of the ways in which this notion emerges in the works by Knight, Keynes, Shackle and Davidson. It focuses on the uniqueness of each approach. It is unquestionable that these authors' theories of uncertainty have meaningful resemblances. Nevertheless, although all these treatments share an emphasis on the conceptual distinction between (probabilistic) risk and uncertainty, as well as on their immeasurability, it is fair to say that these authors' approaches to the conceptualisation of uncertainty are distinctive in many respects. Thus, the paper evaluates and contrasts their analyses, concentrating on their peculiarities. It was from this "classical" view of uncertainty (Knight, Keynes, Shackle and Davidson) that a "modern" approach to uncertainty could originally be constructed and further developed, and it is now rooted in current heterodox approaches.
uncertainty; Knight; Keynes; Shackle; Davidson