The same theory that accounts for the love of truth in mathematics and algebra, may be extended to morals, politics, natural philosophy, and other studies, where we consider not the abstract relations of ideas, but their real connexions and existence. But beside the love of knowledge which displays itself in the sciences, there is a certain curiosity implanted in human nature, which is a passion derived from a quite different principle. Some people have an insatiable desire of knowing the actions and circumstances of their neighbours, though their interest be no way concerned in them, and they must entirely depend on others for their information; in which case there is no room for study or application. Let us search for the reason of this phenomenon. It has been proved at large, that the influence of belief is at once to enliven and infix any idea in the imagination, and prevent all kind of hesitation and uncertainty about it. Both these circumstances are advantageous. By the vivacity of the idea we interest the fancy, and produce, though in a lesser degree, the same pleasure which arises from a moderate passion. As the vivacity of the idea gives pleasure, so its certainty prevents uneasiness, by fixing one particular idea in the mind, and keeping it from wavering in the choice of its objects. 'Tis a quality of human nature which is conspicuous on many occasions, and is common both to the mind and body, that too sudden and violent a change is unpleasant to us, and that, however any objects may in themselves be indifferent, yet their alteration gives uneasiness. As 'tis the nature of doubt to cause a variation in the thought, and transport us suddenly from one idea to another, it must of consequence be the occasion of pain. This pain chiefly takes place where interest, relation, or the greatness and novelty of any event interests us in it. 'Tis not every matter of fact of which we have a curiosity to be informed; neither are they such only as we have an interest to know. 'Tis sufficient if the idea strikes on us with such force, and concerns us so nearly, as to give us an uneasiness in its instability and inconstancy. A stranger, when he arrives first at any town, may be entirely indifferent about knowing the history and adventures of the inhabitants; but as he becomes farther acquainted with them, and has lived any considerable time among them, he acquires the same curiosity as the natives. When we are reading the history of a nation, we may have an ardent desire of clearing up any doubt or difficulty that occurs in it; but become careless in such researches, when the ideas of these events are, in a great measure, obliterated. BOOK III. OF MORALS. PART I. OF VIRTUE AND VICE IN GENERAL. SECTION I. MORAL DISTINCTIONS NOT DERIVED FROM REASON.