Suppose two objects to be presented to us, of which the one is the cause and the other the effect; 'tis plain that, from the simple consideration of one, or both these objects, we never shall perceive the tie by which they are united, or be able certainly to pronounce, that there is a connexion betwixt them. 'Tis not, therefore, from any one instance, that we arrive at the idea of cause and effect, of a necessary connexion of power, of force, of energy, and of efficacy. Did we never see any but particular conjunctions of objects, entirely different from each other, we should never be able to form any such ideas. But, again, suppose we observe several instances in which the same objects are always conjoined together, we immediately conceive a connexion betwixt them, and begin to draw an inference from one to another. This multiplicity of resembling instances, therefore, constitutes the very essence of power or connexion, and is the source from which the idea of it arises. In order, then, to understand the idea of power, we must consider that multiplicity; nor do I ask more to give a solution of that difficulty, which has so long perplexed us. For thus I reason. The repetition of perfectly similar instances can never _alone_ give rise to an original idea, different from what is to be found in any particular instance, as has been observed, and as evidently follows from our fundamental principle, _that all ideas are copied from impressions_. Since, therefore, the idea of power is a new original idea, not to be found in any one instance, and which yet arises from the repetition of several instances, it follows, that the repetition _alone_ has not that effect, but must either _discover_ or _produce_ something new, which is the source of that idea. Did the repetition neither discover nor produce any thing new, our ideas might be multiplied by it, but would not be enlarged above what they are upon the observation of one single instance. Every enlargement, therefore, (such as the idea of power or connexion) which arises from the multiplicity of similar instances, is copied from some effects of the multiplicity, and will be perfectly understood by understanding these effects. Wherever we find any thing new to be discovered or produced by the repetition, there we must place the power, and must never look for it in any other object.