to depend upon an intricate Machinery or secret Structure, of Parts, we make no Difficulty to attribute all our Knowledge of it to Experience. Who will assert, that he can give the ultimate Reason, why Milk or Bread is proper Nourishment for a Man, not for a Lyon or a Tyger?
But the same Truth may not appear, at first View, to have the same Evidence with regard to Events, which have become familiar to us from our first Appearance in the World, which bear a close Analogy to the whole Course of Nature, and which are suppos'd to depend on the simple Qualities of Objects, without any secret Structure of Parts. We are apt to imagine, that we could discover these Effects, by the mere Operations of our Reason, without Experience. We fancy, that, were we brought, of a sudden, into this World, we could at first have infer'd, that one Billiard-ball would communicate Motion to another upon Impulse; and that we needed not to have waited for the Event, in order to pronounce with Certainty concerning it. Such is the Influence of Custom, that, where it is strongest, it not only covers our natural Ignorance, but even conceals itself, and seems not to take place, merely because it is found in the highest Degree.
But
