But from its circulation in frogs and fishes, it is only a presumption, though a strong one, from analogy, that it takes place in men and other animals.

The analogical reasoning is much weaker, when we infer the circulation of the sap in vegetables from our experience that the blood circulates in animals; and those, who hastily followed that imperfect analogy, are found, by more accurate experiments, to have been mistaken.
If we see a house, CLEANTHES, we conclude, with the greatest certainty, that it had an architect or builder; because this is precisely that species of effect which we have experienced to proceed from that species of cause.

But surely you will not affirm, that the universe bears such a resemblance to a house, that we can with the same certainty infer a similar cause, or that the analogy is here entire and perfect.

The dissimilitude is so striking, that the utmost you can here pretend to is a guess, a conjecture, a presumption concerning a similar cause; and how that pretension will be received in the world, I leave you to consider.
It would surely be very ill received, replied CLEANTHES; and I should be deservedly blamed and detested, did I allow, that the proofs of a Deity amounted to no more than a guess or conjecture.

But is the whole adjustment of means to ends in a house and in the universe so slight a resemblance?
The economy of final causes?
The order, proportion, and arrangement of every part?
Steps of a stair are plainly contrived, that human legs may use them in mounting; and this inference is certain and infallible.