One historical peculiarity of the debates over reason is the fact that, although Paley's Natural Theology is a long defense of the argument from design, Paley never even mentions David Hume’s famous logical demolition of that argument, in Dialogues concerning Natural Religion (1779). For one thing, Paley’s views were well-formed by the time he wrote. More importantly, it was widely held among British intellectuals that Hume’s arguments were unconvincing. Hume’s impact was greater in the 1800s, his ideas appearing in a variety of empirical and skeptical treatments of knowledge. Acknowledging that in the 1700s thoroughly skeptical philosophy was a minority view, Hume (1711-1776) still serves as a good example for us of the impact of science and empirical reasoning.

Hume’s argument nicely outlines the alternatives. He also provides an example of how empirical rationalism could be taken to one end of the spectrum of views on religion. For Hume, the foundation of knowledge is empirical experience. Sensory experiences are all isolated states, and our ideas about the world and causes are ideas about the connections among experiences. However, he thought that human understanding can never discover real connections, and so never confirm beliefs. This put him at odds with both traditional theological reasoning and with the newer theological arguments from design. The older view, and traditionally the foremost intellectual defense of religion, was that God can be known to exist by reason, but that our human understanding is inadequate to comprehend His attributes and actions. Newtonian natural theology took the opposite tack, that the only proof of the existence of the deity is the argument from design. It was sufficient proof, but human reason could also determine His attributes through the evidences of nature. To deny this would be atheism.

Hume’s skeptical view used principles of reasoning to undercut both theological views. Agreeing that an empirical argument was the only true approach to knowledge, as matters of fact, and so the traditional view is rejected. He then proceeds to demonstrate that the necessity of a designer cannot be confirmed by empirical experience, just as we cannot truly determine ultimate causes. Thus we’re left with no possible proof of the existence of God, with a suspension of judgment as the only reasonable position.

Excerpts from David Hume, Dialogues concerning Natural Religion [quotations from the Works (1854), ed. Kemp Smith]

The work is constructed as a dialogue, with each character representing a philosophical position.

The view of Philo [the empiricist skeptic], that reason alone cannot provide proof:

"The vulgar, indeed, we may remark, who are unacquainted with science and profound enquiry, observing the endless disputes of the learned, have commonly a thorough contempt for philosophy; and rivet themselves the faster, by that means, in the great points of theology which have been taught them. Those who enter a little into study and enquiry, finding many appearances of evidence in doctrines the newest and most extraordinary, think nothing too difficult for human reason; and, presumptuously breaking through all fences, profane the inmost sanctuaries of the temple. But Cleanthes will, I hope, agree with me, that, after we have abandoned ignorance, the surest remedy, there is still one expedient left to prevent this profane liberty. Let Demea's principles be improved and cultivated: let us become thoroughly sensible of the weakness, blindness, and narrow limits of human reason: let us duly consider its uncertainty and endless contrarieties, even in subjects of common life and practice: let the errors and deceits of our very senses be set before us; the insuperable difficulties which attend first principles in all systems; the contradictions which adhere to the very ideas of matter, cause and effect, extension, space, time, motion; and in a word, quantity of all kinds, the object of the only science that can fairly pretend to any certainty or evidence. When these topics are displayed in their full light, as they are by some philosophers and almost all divines; who can retain such confidence in this frail faculty of reason as to pay any regard to its determinations in points so sublime, so abstruse, so remote from common life and experience? When the coherence of the parts of a stone, or even that composition of parts which renders it extended; when these familiar objects, I say, are so inexplicable, and contain circumstances so repugnant and contradictory; with what assurance can we decide concerning the origin of worlds, or trace their history from eternity to eternity?" [p. 131]

Demea’s [the orthodox traditionalist] response, that divine attributes are beyond our comprehension:

"No man, no man at least of common sense, I am persuaded, ever entertained a serious doubt with regard to a truth so certain and self-evident [as the Being of a God]. The question is not concerning the BEING, but the NATURE of GOD. This, I affirm, from the infirmities of human understanding, to be altogether incomprehensible and unknown to us. The essence of that supreme Mind, his attributes, the manner of his existence, the very nature of his duration; these, and every particular which regards so divine a Being, are mysterious to men. Finite, weak, and blind creatures, we ought to humble ourselves in his august presence; and, conscious of our frailties, adore in silence his infinite perfections, which eye hath not seen, ear hath not heard, neither hath it entered into the heart of man to conceive. They are covered in a deep cloud from human curiosity. It is profaneness to attempt penetrating through these sacred obscurities. And, next to the impiety of denying his existence, is the temerity of prying into his nature and essence, decrees and attributes." [p. 141]

Philo’s rejoinder, agreeing on reason’s limitation only to reject Demea’s reasoning that we have to accept incomprehensibility:

"Our ideas reach no further than our experience. We have no experience of divine attributes and operations. I need not conclude my syllogism. You can draw the inference yourself. And it is a pleasure to me (and I hope to you too) that just reasoning and sound piety here concur in the same conclusion, and both of them establish the adorably mysterious and incomprehensible nature of the Supreme Being." [p. 142]

Cleanthes’s [a cautious philosopher] use of the mechanist philosophy to provide the traditional basis for an empirical argument from design:

"Look round the world: contemplate the whole and every part of it: you will find it to be nothing but one great machine, subdivided into an infinite number of lesser machines, which again admit of subdivisions to a degree beyond what human senses and faculties can trace and explain. All these various machines, and even their most minute parts, are adjusted to each other with an accuracy which ravishes into admiration all men who have ever contemplated them. The curious adapting of means to ends, throughout all nature, resembles exactly, though it much exceeds, the productions of human contrivance; of human designs, thought, wisdom, and intelligence. Since, therefore, the effects resemble each other, we are led to infer, by all the rules of analogy, that the causes also resemble; and that the Author of Nature is somewhat similar to the mind of man, though possessed of much larger faculties, proportioned to the grandeur of the work which he has executed. By this argument a posteriori, and by this argument alone, do we prove at once the existence of a Deity, and his similarity to human mind and intelligence." [p. 143]

But Philo rejects the analogy of mind or intelligence at work, because we are so limited in our experience, and makes an argument for prudent suspension of judgment:

"And can you blame me, Cleanthes, if I here imitate the prudent reserve of Simonides, who, according to the noted story, being asked by Hiero, What God was? desired a day to think of it, and then two days more; and after that manner continually prolonged the term, without ever bringing in his definition or description? Could you even blame me, if I answered at first, that I did not know, and was sensible that this subject lay vastly beyond the reach of my faculties? You might cry out sceptic and rallier, as much as you pleased: but having found, in so many other subjects much more familiar, the imperfections and even contradictions of human reason, I never should expect any success from its feeble conjectures, in a subject so sublime, and so remote from the sphere of our observation. When two species of objects have always been observed to be conjoined together, I can infer, by custom, the existence of one wherever I see the existence of the other; and this I call an argument from experience. But how this argument can have place, where the objects, as in the present case [the entire universe], are single, individual, without parallel, or specific resemblance, may be difficult to explain. And will any man tell me with a serious countenance, that an orderly universe must arise from some thought and art like the human, because we have experience of it? To ascertain this reasoning, it were requisite that we had experience of the origin of worlds; and it is not sufficient, surely, that we have seen ships and cities arise from human art and contrivance." [p. 149]

Philo’s skeptical argument against inferring a perfect designer, and the ability to discern any specific attributes of such a designer:

"But were this world ever so perfect a production, it must still remain uncertain, whether all the excellences of the work can justly be ascribed to the workman. If we survey a ship, what an exalted idea must we form of the ingenuity of the carpenter who framed so complicated, useful, and beautiful a machine? And what surprize must we feel, when we find him a stupid mechanic, who imitated others, and copied an art, which, through a long succession of ages, after multiplied trials, mistakes, corrections, deliberations, and controversies, had been gradually improving? Many worlds might have been botched and bungled, throughout an eternity, ere this system was struck out; much labour lost, many fruitless trials made; and a slow, but continued improvement carried on during infinite ages in the art of world-making. In such subjects, who can determine, where the truth; nay, who can conjecture where the probability lies, amidst a great number of hypotheses which may be proposed, and a still greater which may be imagined?

And what shadow of an argument, continued Philo, can you produce, from your hypothesis, to prove the unity of the Deity? A great number of men join in building a house or ship, in rearing a city, in framing a commonwealth; why may not several deities combine in contriving and framing a world? This is only so much greater similarity to human affairs. By sharing the work among several, we may so much further limit the attributes of each, and get rid of that extensive power and knowledge, which must be supposed in one deity, and which, according to you, can only serve to weaken the proof of his existence. And if such foolish, such vicious creatures as man, can yet often unite in framing and executing one plan, how much more those deities or demons, whom we may suppose several degrees more perfect! [p. 167]

. . . But further, Cleanthes: men are mortal, and renew their species by generation; and this is common to all living creatures. The two great sexes of male and female, says Milton, animate the world. Why must this circumstance, so universal, so essential, be excluded from those numerous and limited deities? Behold, then, the theogony of ancient times brought back upon us.

And why not become a perfect Anthropomorphite? Why not assert the deity or deities to be corporeal, and to have eyes, a nose, mouth, ears, etc.? Epicurus maintained, that no man had ever seen reason but in a human figure; therefore the gods must have a human figure. And this argument, which is deservedly so much ridiculed by Cicero, becomes, according to you, solid and philosophical.

In a word, Cleanthes, a man who follows your hypothesis is able perhaps to assert, or conjecture, that the universe, sometime, arose from something like design: but beyond that position he cannot ascertain one single circumstance; and is left afterwards to fix every point of his theology by the utmost license of fancy and hypothesis. This world, for aught he knows, is very faulty and imperfect, compared to a superior standard; and was only the first rude essay of some infant deity, who afterwards abandoned it, ashamed of his lame performance: it is the work only of some dependent, inferior deity; and is the object of derision to his superiors: it is the production of old age and dotage in some superannuated deity; and ever since his death, has run on at adventures, from the first impulse and active force which it received from him. You justly give signs of horror, Demea, at these strange suppositions; but these, and a thousand more of the same kind, are Cleanthes's suppositions, not mine. From the moment the attributes of the Deity are supposed finite, all these have place. And I cannot, for my part, think that so wild and unsettled a system of theology is, in any respect, preferable to none at all." [p. 168]

A further argument Philo gives against the analogy of human mind and a designer, removing the discernment of divine attribute of benevolence in nature, is to point to a litany of misery and suffering in both the animal and human world. Given the observed world, how can one

". . . assert the moral attributes of the Deity, his justice, benevolence, mercy, and rectitude, to be of the same nature with these virtues in human creatures? His power we allow is infinite: whatever he wills is executed: but neither man nor any other animal is happy: therefore he does not will their happiness. His wisdom is infinite: he is never mistaken in choosing the means to any end: but the course of Nature tends not to human or animal felicity: therefore it is not established for that purpose. Through the whole compass of human knowledge, there are no inferences more certain and infallible than these. In what respect, then, do his benevolence and mercy resemble the benevolence and mercy of men?" [p. 198]

And on purpose in Nature:

'But what, I beseech you, is the object of that curious artifice and machinery, which she has displayed in all animals? The preservation alone of individuals, and propagation of the species. It seems enough for her purpose, if such a rank be barely upheld in the universe, without any care or concern for the happiness of the members that compose it. No resource for this purpose: no machinery, in order merely to give pleasure or ease: no fund of pure joy and contentment: no indulgence, without some want or necessity accompanying it. At least, the few phenomena of this nature are overbalanced by opposite phenomena of still greater importance. "[p. 198]

Philo’s final, pragmatic conclusion:

'If the whole of Natural Theology, as some people seem to maintain, resolves itself into one simple, though somewhat ambiguous, at least undefined proposition, That the cause or causes of order in the universe probably bear some remote analogy to human intelligence: if this proposition be not capable of extension, variation, or more particular explication: if it affords no inference that affects human life, or can be the source of any action or forbearance: and if the analogy, imperfect as it is, can be carried no further than to the human intelligence, and cannot be transferred, with any appearance of probability, to the qualities of the mind; if this really be the case, what can the most inquisitive, contemplative, and religious man do more than give a plain, philosophical assent to the proposition, as often as it occurs, and believe that the arguments on which it is established exceed the objections which lie against it? Some astonishment, indeed, will naturally arise from the greatness of the object; some melancholy from its obscurity; some contempt of human reason, that it can give no solution more satisfactory with regard to so extraordinary and magnificent a question." [p. 227]