It appears, then, that this Idea of a necessary Connexion amongst Objects or Events arises from a Number of similar Instances of the constant Conjunction of these Events, and can never be suggested by any one of these Instances, survey'd in all possible Lights and Positions. But what is there in a Number of Instances, different from every single Instance, which is suppos'd to be exactly similar? Nothing but this, that after a Repetition of similar Instances, the Mind is carry'd by Habit, upon the Appearance of one Event, to expect its usual Attendant, and to believe, that it will exist. This Connexion, therefore, which we feel in the Mind, or customary Transition of the Imagination from one Object to its usual Attendant, is the only Sentiment or Impression, from which we form the Idea of Power or necessary Connexion. Nothing farther is in the Case. Contemplate the Subject on all Sides, you will never find any other Origin of this Idea. There is no other Difference betwixt one Instance, from which we never can receive the Idea of Connexion, and a Number of similar Instances, by which it is suggested. The first Time a Man saw the Communication of Motion by Impulse, as by the Shock of two Billiard-balls, he could not pronounce that the one Effect was connected; but only that it was conjoin'd, with the other. After he has observ'd se-veral
