Labour, upon whichever of those operations it be bestowed, is productive, because it concurs in the creation of a product. Thus the labour of the philosopher, whether experimental or literary, is productive; the labour of the adventurer or master-manufacturer is productive, although he perform no actual manual work; the labour of every operative workman is productive, from the common day-labourer in agriculture, to the pilot that governs the motion of a ship.
Book I, On Production, Chapter VII, p. 85 - A Treatise On Political Economy (Fourth Edition) (1832)
