"Neo-classical economics also considered other factors which influence the development of the national economy, e.g., the growth of population, changes in consumer preferences, and technical progress. Technical progress, however, is treated as a phenomenon outside the field of economics, influencing the process of economic development only by chance, and not being involved with it organically. Keynes' theory did not fundamentally change any of the views which concern the mechanism of economic development. According to Keynes, the division between accumulation and consumption is also determined on the basis of a marginal psychological calculation. But in his theory, another factor is taken into account, namely, the tendency for capital owners to hold back a certain part of their incomes in a liquid form i.e., as money and other means of payment. This introduces certain complications, since besides the decision as to what part of the income should be allocated for consumption and what part for accumulation, a third consideration is brought in, namely, what is to be done with accumulated wealth: should it be saved or invested, or should it be retained in a monetary form. The great differences in the division of incomes in the capitalist system in principle accelerate economic development. However, according to Keynes, complications arise since some of the capital owners hold back money in a liquid form. Part of the labour force and of the productive capacity are thus made to lie idle, and the productive forces of society are squandered."