Smith's realization of the interdependence of land, labour, and capital was a real breakthrough. He noted that workers and landowners tend to consume their incomes, while employers are more frugal, investing their savings in capital stock. He saw that wage rates vary, depending on different levels of "skill, dexterity, and judgement", and that there are two forms of labour : productive (engaged in agriculture or manufacturing) and what he called "unproductive" (supplying services needed to back up the main work). The highly unequal outcomes of today's market system are some way from what Smith envisaged.