Enquiry Concerning Political Justice-第91章

Let us enquire then into the nature and origin of general principles. Engaged, as men are, in perpetual intercourse with their neighbours, and constantly liable to be called upon without the smallest previous notice, in cases where the interest of their fellows is deeply involved, it is not possible for them, upon all occasions, to deduce, through a chain of reasoning, the judgement which should be followed. Hence the necessity of resting-places for the mind, of deductions, already stored in the memory, and prepared for application as circumstances may demand. We find this necessity equally urgent upon us in matters of science and abstraction as in conduct and morals. Theory has also a further use. It serves as a perpetual exercise and aliment to the understanding, and renders us competent and vigorous to judge in every situation that can occur. Nothing can be more idle and shallow than the competition which some men have set up between theory and practice. It is true that we can never predict, from theory alone, the success of any given experiment. It is true that no theory, accurately speaking, can possibly be practical. It is the business of theory to collect the circumstances of a certain set of cases, and arrange them. It would cease to be theory if it did not leave out many circumstances; it collects such as are general, and leaves out such as are particular. In practice however, those circumstances inevitably arise which are necessarily omitted in the general process: they cause the phenomenon, in various ways, to include features which were not in the prediction, and to be diversified in those that were. Yet theory is of the highest use; and those who decry it may even be proved not to understand themselves. They do not mean that men should always act in a particular case, without illustration from any other case, for that would be to deprive us of all understanding. The moment we begin to compare cases, and infer, we begin to theorize; no two things in the universe were ever perfectly alike. The genuine exercise of man therefore is to theorize, for this is, in other words, to sharpen and improve his intellect; but not to become the slave of theory, or at any time to forget that it is, by its very nature, precluded from comprehending the whole of what claims our attention.