If its weakness render it obscure, 'tis our business to remedy that defect, as much as possible, by keeping the idea steady and precise; and till we have done so, 'tis in vain to pretend to reasoning and philosophy. [1] Part I. Sect. 5. SECTION 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, 'twill 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. 'Tis only _causation_, which produces such a connexion, as to give us assurance from the existence or action of one object, that 'twas followed or preceded by any other existence or action; nor can the other two relations ever be made use of in reasoning, except so far as they either affect or are affected by it. There is nothing in any objects to persuade 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,