Were emotions of the same nature with colour and figure, to continue in their present state till varied by some operating cause, the condition of man would be deplorable. It is ordered wisely, that emotions should more resemble another attribute of matter, _viz._ motion, which requires the constant exertion of an operating cause, and ceases when the cause is withdrawn. An emotion may subsist while its cause is present; and when its cause is removed, may subsist by means of an idea, though in a fainter degree. But the moment another thought breaks in and occupies the mind, so as to exclude not only this cause, but also its idea, the emotion is gone: it is no longer felt. If it return with its cause or idea, it again vanisheth with them when other thoughts crowd in. This observation is applicable to emotions and passions of every kind. And these accordingly are connected with perceptions and ideas, so intimately as not to have any independent existence. A strong passion, it is true, hath a mighty influence to detain its object in the mind; but not so as to detain it for ever. A succession of perceptions or ideas is unavoidable[32]: the object of the passion may be often recalled; but however interesting, it must by intervals yield to other objects. For this reason, a passion rarely continues long with an equal degree of vigour. It is felt strong and moderate, in a pretty quick succession. The same object makes not always the same impression; because the mind, being of a limited capacity, cannot, at the same instant, give great attention to a plurality of objects. The strength of a passion depends on the impression made by its cause; and a cause makes its strongest impression, when happening to be the single interesting object, it attracts our whole attention[33]. Its impression is slighter when our attention is divided betwixt it and other objects; and at that time the passion is slighter in proportion.