Three professors at Glasgow University in the eighteenth century argued that the economic aspects of slavery were the most likely to see the demise of the institution of slavery. Adam Smith was the most forceful of the three, and on empirical grounds he asserted that although slavery might appear cheap, in reality it was the dearest form of labour, due to there being no incentive for slaves to work, unlike free waged labour's prospect of reward. In addition, slaves were neither innovative nor inventive and did not contribute to growth and prosperity. Linking the question of slavery to the size of population, Hume, Robert Wallace, Sir James Steuart and Montesquieu made significant contributions to the debate, comparing the populations of the Ancient World with those of the eighteenth century. The end of the institution was brought about in no small measure by the arguments of the philosophers, when slavery was legally abolished in the countries of Europe and in America.