I intend to examine this point under each of these heads in their order.

But before I proceed further, I hope it will not be thought amiss, if I lay down the rules which governed me in this inquiry, and which have misled me in it, if I have gone astray.1.If two bodies produce the same or a similar effect on the mind, and on examination they are found to agree in some of their properties, and to differ in others; the common effect is to be attributed to the properties in which they agree, and not to those in which they differ.2.Not to account for the effect of a natural object from the effect of an artificial object.
3.

Not to account for the effect of any natural object from a conclusion of our reason concerning its uses, if a natural cause may be assigned.
4.

Not to admit any determinate quantity, or any relation of quantity, as the cause of a certain effect, if the effect is produced by different or opposite measures and relations; or if these measures and relations may exist, and yet the effect may not be produced.

These are the rules which I have chiefly followed, whilst I examined into the power of proportion considered as a natural cause; and these, if he thinks them just, I request the reader to carry with him throughout the following discussion; whilst we inquire, in the first place, in what things we find this quality of beauty; next, to see whether in these we can find any assignable proportions in such a manner as ought to convince us that our idea of beauty results from them.