The Austrian School argues that this fundamental theory of classical economics is false and prefers the subsequent and modern subjective theory of value put forward by Carl Menger in his book "Principles of Economics". The Austrian School was not alone in criticizing the Marxian and classical belief in the labor theory of value. British economist Alfred Marshall attacked Marx, saying: "It is not true that the spinning of yarn in a factory [...] is the product of the labour of the operatives. It is the product of their labour, together with that of the employer and subordinate managers, and of the capital employed". Marshall points to the capitalist as sacrificing the money he could be using now for investment in business, which ultimately produces work. By this logic, the capitalist contributes to the work and productivity of the factory because he delays his gratification through investment. Through the law of supply and demand, Marshall attacked Marxian theory of value. According to Marshall, price or value is determined not just by supply, but by the demand of the consumer. Labor does contribute to cost, but so do the wants and needs of consumers. The shift from labor being the source of all value to subjective individual evaluations creating all value undermines Marx's economic conclusions and some of his social theories.