Impressions and ideas differ only in their strength and vivacity.

The foregoing conclusion is not founded on any particular degree of vivacity.

It cannot therefore be affected by any variation in that particular.

An idea is a weaker impression; and as a strong impression must necessarily have a determinate quantity and quality, the case must be the same with its copy or representative.
Thirdly, it is a principle generally received in philosophy that everything in nature is individual, and that it is utterly absurd to suppose a triangle really existent, which has no precise proportion of sides and angles.

If this therefore be absurd in fact and reality, it must also be absurd in idea; since nothing of which we can form a clear and distinct idea is absurd and impossible.