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.