I observe Iris Murdoch's distinctive use of the word ‘flux’ in discussion of Sartre's Nausea and show that her usage is persuasive and revolutionary, first as Sartre exegesis, second as Heraclitus exegesis, and throughout as a contribution to the philosophy of language. Murdoch's usage of ‘flux’ frames a comparison of Sartre's Roquentin with other figures who have had similarly flowing experience but without nausea. Roquentin's plight is shown to be ‘a philosopher's plight’ precipitated by a defective theory of descriptive success. I then show how the Heraclitean fragments would support Murdoch's treatment of flux and on close analysis contradict the established view exemplified in the work of Wittgenstein and Jonathan Barnes. Flux is not a variety of change, and the river image ‘cannot be analysed into non-metaphorical components without a loss of substance’.