use of terms before we were able exactly to define them, or fix their meaning. We shall now correct this fault by giving a precise definition of cause and effect.
There may two definitions be given of this relation, which are only different, by their presenting a different view of the same object, and making us consider it either as a philosophical or as a natural relation; either as a comparison of two ideas, or as an association betwixt them. We may define a CAUSE to be An object precedent and contiguous to another, and where all the objects resembling the former are placed in like relations of precedency and contiguity to those objects that resemble the latter. I If this definition be esteemed defective, because drawn from objects foreign to the cause, we may substitute this other definition in its place, viz. A CAUSE is an object precedent and contiguous to another, and so united with it, that the idea, of the one determines the mind to form the idea of the other, and the impression of the one to form a more lively idea of the other. 2 should this definition also be rejected for the same reason, I know no other remedy, than that the persons, who express this delicacy, should substitute a juster definition in its place. But for my part I must own my incapacity for such an undertaking. When I examine with the utmost accuracy those objects, which are commonly denominated causes and effects, I find, in considering a single instance, that the one object is precedent and contiguous to the other; and in inlarging my view to consider several instances, I find only, that like objects are constantly placed in like relations of succession and contiguity. Again, when I consider the influence of this constant conjunction, I perceive, that such a relation can never be an object of reasoning, and can never operate upon the mind, but by means of custom, which determines the imagination to make a transition from the idea of one object to that of its usual attendant, and from the impression of one to a more lively idea of the other. However extraordinary these sentiments may appear, I think it fruitless to trouble myself with any farther enquiry or reasoning upon the subject, but shall repose myself on them as on established maxims.
It will only be proper, before we leave this subject, to draw some corrollaries from it, by which we may remove several prejudices and popular errors, that have very much prevailed in philosophy. First, We may learn from the foregoing, doctrine, that all causes are of the same kind, and that in particular there is no foundation for that distinction, which we sometimes make betwixt efficient causes and causes sine qua non; or betwixt efficient causes, and formal, and material, and exemplary, and final causes. For as our idea of efficiency is derived from the constant conjunction of two objects, wherever this is observed, the cause is efficient; and where it is not, there can never be a cause of any kind. For the same reason we must reject the distinction betwixt cause and occasion, when supposed to signify any thing essentially different from each other. If constant conjunction be implyed in what we call occasion, it is a real cause. If not, it is no relation at all, and cannot give rise to any argument or reasoning.