THE motions of the heart of man are infinitely various: The different forms and shapes, in which our passions appear, the sudden and secret turns and windings of them through the heart, with the strange mixtures and complications of them, in their continual exercise, are innumerable and nameless. It is as hard, almost, to reduce them to a perfect scheme, and to range all their excursions into exact order of science, as it is to bring them under complete government in practice.
Yet, since it is of such vast importance in human life, to regulate their motions, that they may not become utterly exorbitant and mischievous, I thought it proper, for this end, to make a diligent enquiry into the nature of these mingled powers of flesh and spirit, to take a survey of them in a comprehensive view, and draw them into a little system. With no small care, I have attempted, to range them in some tolerable order and method under general names, to trace out and observe their causes, their effects, their influences on human affairs, and the various purposes which they serve in the life of man. This is not only desirable, as it is a part of the science of human nature, or the knowledge of ourselves, without which, we can never pretend to be philosophers; but this may also give us some assistance toward the forming proper rules for their better management, and the bringing these active and restless promoters, or disturbers of our happiness, under a moral and religious discipline; and without this, we can neither be men of wisdom nor piety.