We assess the actual relevance of Robbins' paper ‘On the elasticity of Demand for Income in terms of Effort’ to the theory of work supply. First, we show that the paper is the first application of income and substitution effects to this branch of economic research. Next, we analyse Robbins' economic terminology, especially his definition of work. We find that the concept of work he uses could seem vague as he may be considering both the length and intensity dimensions of this activity. To verify this possibility, we formally reassess Robbins' original proposal by introducing this wider definition of work into the mathematical framework he proposes. The resulting model shows that this reading (i) is compatible with his diagrammatic analysis; (ii) clarifies the meaning of the other vague economic concepts the author uses; and (iii) illuminates his verbal explanations. Additionally, we derive all the relevant results of both the income-leisure and the more recent effort-extraction models from this Robbinsian model of work supply. This last outcome allows us to state that Robbins' model comprises current theories of work supply.