The prime postulate of evolutionary science, the preconception constantly underlying the inquiry, is the notion of a cumulative causal sequence; and writers on economics are in the habit of recognising that the phenomena with which they are occupied are subject to such a law of development. The preconception of the utilitarians, in substance the natural-rights preconception, that unrestrained human conduct will result in the greatest human happiness, retains so much of its force in Cairnes's time as is implied in the then current assumption that what is normal is also right. The associationists, to whom economics owes its transition from the older classical phase to the modern or quasi-classical, chose as their guiding point of view the metaphysical postulate of congruity, in substance, the 'similarity' of the associationist theory of knowledge. The laws of the science, that which makes up the economist's theoretical knowledge, are laws of the normal case.