| 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. |
| The examination of the impression bestows a clearness on the idea; and the examination of the idea bestows a like clearness on all our reasoning. |
| Let us therefore cast our eye on any two objects, which we call cause and effect, and turn them on all sides, in order to find that impression, which produces an idea, of such prodigious consequence. |
| At first sight I perceive, that I must not search for it in any of the particular qualities of the objects; since. |
| which-ever of these qualities I pitch on, I find some object, that is not possessed of it, and yet falls under the denomination of cause or effect. |
| And indeed there is nothing existent, either externally or internally, which is not to be considered either as a cause or an effect; though it is plain there is no one quality, which universally belongs to all beings, and gives them a title to that denomination. |