The exactly similarity of the cases gives us a perfect assurance of a similar event; and a stronger evidence is never desired nor sought after. But wherever you depart, in the least, from the similarity of the cases, you diminish proportionably the evidence; and may at last bring it to a very weak analogy, which is confessedly liable to error and uncertainty. After having experienced the circulation of the blood in human creatures, we make no doubt, that it takes place in Titius and Maevius: 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?23 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. Human legs are also contrived for walking and mounting; and this inference, I allow, is not altogether so certain, because of the dissimilarity which you remark; but does it, therefore, deserve the name only of presumption or conjecture?

Good God! cried Demea, interrupting him, where are we? Zealous defenders of religion allow, that the proofs of a deity fall short of perfect evidence! And you, Philo, on whose assistance I depended, in proving the adorable mysteriousness of the divine nature, do you assent to all these extravagant opinions of Cleanthes? For what other name can I give them? Or why spare my censure, when such principles are advanced, supported by such an authority, before so young a man as Pamphilus?

You seem not to apprehend, replied Philo, that I argue with Cleanthes in his own way; and by showing him the dangerous consequences of his tenets, hope at last to reduce him to our opinion. But what sticks most with you, I observe, is the representation which Cleanthes has made of the argument a posteriori; and finding that that argument is likely to escape your hold and vanish into air, you think it so disguised that you can scarcely believe it to be set in its true light. Now, however much I may dissent, in other respects, from the dangerous principle of Cleanthes, I must allow, that he has fairly represented that argument; and I shall endeavour so to state the matter to you that you will entertain no farther scruples with regard to it.

Were a man to abstract from everything which he knows or has seen, he would be altogether incapable, merely from his own ideas, to determine what kind of scene the universe must be, or to give the preference to one state or situation of things above another. For as nothing which he clearly conceives could be esteemed impossible or implying a contradiction, every chimera of his fancy would be upon an equal footing; nor could he assign any just reason, why he adheres to one idea or system, and rejects the others, which are equally possible.

Again; after he opens his eyes, and contemplates the world as it really is, it would be impossible for him, at first, to assign the cause of any one event, much less, of the whole of things or of the universe. He might set his fancy a-rambling; and she might bring him in an infinite variety of reports and representations. These would all be possible; but being all equally possible, he would never, of himself, give a satisfactory account for his preferring one of them to the rest. Experience alone can point out to him the true cause of any phenomenon.24

Now, according to this method of reasoning, Demea, it follows (and is, indeed, tacitly allowed by Cleanthes himself) that order, arrangement, or the adjustment of final causes is not, of itself, any proof of design; but only so far as it has been experienced to proceed from that principle. For aught we can know a priori, matter may contain the source or spring of order originally, within itself, as well as mind does; and there is no more difficulty in conceiving, that the several elements, from an internal unknown cause, may fall into the most exquisite arrangement, than to conceive that their ideas, in the great, universal mind, from a like internal, unknown cause, fall into that arrangement. The equal possibility of both these suppositions is allowed. But by experience we find (according to Cleanthes), that there is a difference between them. Throw several pieces of steel together, without shape or form; they will never arrange themselves so as to compose a watch: Stone, and mortar, and wood, without an architect, never erect a house. But the ideas in a human mind, we see, by an unknown, inexplicable economy, arrange themselves so as to form the plan of a watch or house. Experience, therefore, proves, that there is an orginal principle of order in mind, not in matter. From similar effects we infer similar causes. The adjustment of means to ends is alike in the universe, as in a machine of human contrivance. The causes, therefore, must be resembling.

I was from the beginning scandalized, I must own, with this resemblance, which is asserted, between the deity and human creatures; and must conceive it to imply such a degradation of the supreme being as no sound theist could endure. With your assistance, therefore, Demea, I shall endeavour to defend what you justly call the adorable mysteriousness of the divine nature, and shall refute this reasoning of Cleanthes; provided he allows, that I have made a fair representation of it.

When Cleanthes has assented, Philo, after a short pause, proceeded in the following manner.

That all inferences, Cleanthes, concerning fact are founded on experience, and that all experimental reasonings are founded on the supposition, that similar causes prove similar effects, and similar effects similar causes; I shall not, at present, much dispute with you. But observe, I entreat you, with what extreme caution all just reasoners proceed in the transferring of experiments to similar cases. Unless the cases be exactly similar, they repose no perfect confidence in applying their past observation to any particular phenomenon. Every alteration of circumstances occasions a doubt concerning the event; and it requires new experiments to prove certainly, that the new circumstances are of no moment or importance.25 A change in bulk, situation, arrangement, age, disposition of the air, or surrounding bodies; any of these particulars may be attended with the most unexpected consequences: And unless the objects be quite familiar to us, it is the highest temerity to expect with assurance, after any of these changes, an event similar to that which before fell under our observation. The slow and deliberate steps of philosophers here, if anywhere, are distinguished from the precipitate march of the vulgar, who, hurried on by the smallest similitude, are incapable of all discernment or consideration.

But can you think, Cleanthes, that your usual phlegm and philosophy have been preserved in so wide a step as you have taken, when you compared to the universe houses, ships, furniture, machines; and from their similarity in some circumstances inferred a similarity in their causes? Thought, design, intelligence, such as we discover in men and other animals, is no more than one of the springs and principles of the universe, as well as heat or cold, attraction or repulsion, and a hundred others, which fall under daily observation. It is an active cause, by which some particular parts of nature, we find, produce alterations on other parts. But can a conclusion, with any propriety, be transferred from parts to the whole? Does not the great disproportion bar all comparison and inference? From observing the growth of a hair, can we learn anything concerning the generation of a man? Would the manner of a leaf’s blowing, even though perfectly known, afford us any instruction concerning the vegetation of a tree?

But allowing that we were to take the operations of one part of nature upon another for the foundation of our judgement concerning the origin of the whole (which never can be admitted) yet why select so minute, so weak, so bounded a principle as the reason and design of animals is found to be upon this planet? What peculiar privilege has this little agitation of the brain which we call thought, that we must thus make it the model of the whole universe? Our partiality in our own favour does indeed present it on all occasions: But sound philosophy ought carefully to guard against so natural an illusion.

So far from admitting, continued Philo, that the operations of a part can afford us any just conclusion concerning the origin of the whole, I will not allow any one part to form a rule for another part, if the latter be very remote from the former.