| But to destroy this artifice, we need but reflect on that principle so oft insisted on, that all our ideas are copyed from our impressions. |
| For from thence we may immediately conclude, that since all impressions are clear and precise, the ideas, which are copyed from them, must be of the same nature, and can never, but from our fault, contain any thing so dark and intricate. |
| An idea is by its very nature weaker and fainter than an impression; but being in every other respect the same, cannot imply any very great mystery. |
| If its weakness render it obscure, it is our business to remedy that defect, as much as possible, by keeping the idea steady and precise; and till we have done so, it is in vain to pretend to reasoning and philosophy. |
| SECT. II. OF PROBABILITY, AND OF THE IDEA OF CAUSE AND EFFECT. |
| This is all I think necessary to observe concerning those four relations, which are the foundation of science; but as to the other three, which depend not upon the idea, and may be absent or present even while that remains the same, it will be proper to explain them more particularly. |
| These three relations are identity, the situations in time and place, and causation. |
| All kinds of reasoning consist in nothing but a comparison, and a discovery of those relations, either constant or inconstant, which two or more objects bear to each other. |
| This comparison we may make, either when both the objects are present to the senses, or when neither of them is present, or when only one. |
| When both the objects are present to the senses along with the relation, we call this perception rather than reasoning; nor is there in this case any exercise of the thought, or any action, properly speaking, but a mere passive admission of the impressions through the organs of sensation. |
| According to this way of thinking, we ought not to receive as reasoning any of the observations we may make concerning identity, and the relations of time and .place; since in none of them the mind can go beyond what is immediately present to the senses, either to discover the real existence or the relations of objects. |
| It is only causation, which produces such a connexion, as to give us assurance from the existence or action of one object, that it was followed or preceded by any other existence or action; nor can the other two relations be ever made use of in reasoning, except so far as they either affect or are affected by it. |
| There is nothing in any objects to perswade us, that they are either always remote or always contiguous; and when from experience and observation we discover, that their relation in this particular is invariable, we, always conclude there is some secret cause, which separates or unites them. |
| The same reasoning extends to identity. |
| We readily suppose an object may continue individually the same, though several times absent from and present to the senses; and ascribe to it an identity, notwithstanding the interruption of the perception, whenever we conclude, that if we had kept our eye or hand constantly upon it, it would have conveyed an invariable and uninterrupted perception. |
| But this conclusion beyond the impressions of our senses can be founded only on the connexion of cause and effect; nor can we otherwise have any security, that the object is not changed upon us, however much the new object may resemble that which was formerly present to the senses. |
| Whenever we discover such a perfect resemblance, we consider, whether it be common in that species of objects; whether possibly or probably any cause coued operate in producing the change and resemblance; and according as we determine concerning these causes and effects, we form our judgment concerning the identity of the object. |
| Here then it appears, that of those three relations, which depend not upon the mere ideas, the only one, that can be traced beyond our senses and informs us of existences and objects, which we do not see or feel, is causation. |
| This relation, therefore, we shall endeavour to explain fully before we leave the subject of the understanding. |
| To begin regularly, we must consider the idea of causation, and see from what origin it is derived. |
| It is impossible to reason justly, without understanding perfectly the idea concerning which we reason; and it is impossible perfectly to understand any idea, without tracing it up to its origin, and examining that primary impression, from which it arises. |