"Planning and the market do not exclude each other. Planning may utilise the uniformity of behaviour patterns of units operating in the market as one of the means of influencing their decisions. This happens, for instance, when the planning authority imposes tariffs or pays subsidies in order to influence the quantities bought or sold. Sometimes regulation—a special method of planning—is necessary in order to enable the market to achieve co-ordination of the units' decisions. The two methods of co-ordination co-exist with each other. However, in different historic societies, one or the other of these methods plays the preponderant role and appears as the chief means of co-ordinating all the units in the economy. The development of economics as a science is closely connected with the growing preponderance of the market in modern times. The co-ordinating operation of the market and, at times, the failure of the market to achieve co-ordination of decisions have posed the intellectual problems which have led to the emergence and growth of economic science."