SECT.  III.  WHY A CAUSE IS ALWAYS NECESSARY.

To begin with the first question concerning the necessity of a cause:  It is a general maxim in philosophy, that whatever begins to exist, must have a cause of existence.  This is commonly taken for granted in all reasonings, without any proof given or demanded.  It is supposed to be founded on intuition, and to be one of those maxims, which though they may be denyed with the lips, it is impossible for men in their hearts really to doubt of.  But if we examine this maxim by the idea of knowledge above-explained, we shall discover in it no mark of any such intuitive certainty; but on the contrary shall find, that it is of a nature quite foreign to that species of conviction.

All certainty arises from the comparison of ideas, and from the discovery of such relations as are unalterable, so long as the ideas continue the same.  These relations are resemblance, proportions in quantity and number, degrees of any quality, and contrariety; none of which are implyed in this proposition, Whatever has a beginning has also a cause of existence.  That proposition therefore is not intuitively certain.  At least any one, who would assert it to be intuitively certain, must deny these to be the only infallible relations, and must find some other relation of that kind to be implyed in it; which it will then be time enough to examine.

But here is an argument, which proves at once, that the foregoing proposition is neither intuitively nor demonstrably certain.  We can never demonstrate the necessity of a cause to every new existence, or new modification of existence, without shewing at the same time the impossibility there is, that any thing can ever begin to exist without some productive principle; and where the latter proposition cannot be proved, we must despair of ever being able to prove the former.  Now that the latter proposition is utterly incapable of a demonstrative proof, we may satisfy ourselves by considering that as all distinct ideas are separable from each other, and as the ideas of cause and effect are evidently distinct, it will be easy for us to conceive any object to be non-existent this moment, and existent the next, without conjoining to it the distinct idea of a cause or productive principle.  The separation, therefore, of the idea of a cause from that of a beginning of existence, is plainly possible for the imagination; and consequently the actual separation of these objects is so far possible, that it implies no contradiction nor absurdity; and is therefore incapable of being refuted by any reasoning from mere ideas; without which it is impossible to demonstrate the necessity of a cause.