His intellect was profound and comprehensive, thoroughly qualified to grapple with the deepest problems of metaphysics, but by natural preference occupying itself mainly with the practical and moral. Man's conduct in life, not his theory of the universe, was what interested him. The Analogy was written to counteract the practical mischief which he considered wrought by deists and other freethinkers, and the Sermons lay a good deal of stress on everyday Christian duties. His style has frequently been blamed for its obscurity and difficulty, but this is due to two causes: his habit of compressing his arguments into narrow compass, and of always writing with the opposite side of the case in view, so that it has been said of the Analogy that it raises more doubts than it solves. One is also often tempted away from the main course of the argument by the care and precision with which Butler formulates small points of detail.
His great work, The Analogy of Religion, Natural and Revealed, to the Course and Constitution of Nature, cannot be adequately appreciated unless taken in connexion with the circumstances of the period at which it appeared. It was intended as a defence against the great tide of deistical speculation (see Deism), which in the apprehension of many good men seemed likely to sweep away the restraints of religion and make way for a general reign of licence. Butler did not enter the lists in the ordinary way. Most of the literature evoked by the controversy on either side was devoted to rebutting the attack of some individual opponent. Thus it was Bentley versus Collins, Sherlock versus Woolston, Law versus Tindal. The Analogy, on the contrary, did not directly refer to the deists at all, and yet it worked more havoc with their position than all the other books put together, and remains practically the one surviving landmark of the whole dispute. Its central motive is to prove that all the objections raised against revealed or supernatural religion apply with equal force to the whole constitution of nature, and that the general analogy between the principles of divine government, as set forth by the biblical revelation, and those observable in the course of nature, leads us to the warrantable conclusion that there is one Author of both.
Without altogether eschewing Samuel Clarke's a priori system, Butler relies mainly on the inductive method, not professing to give an absolute demonstration so much as a probable proof. And everything is brought into closest relation with "that which is the foundation of all our hopes and of all our fears; all our hopes and fears which are of any consideration; I mean a Future Life."
Butler is a typical instance of the English philosophical mind. He will admit no speculative theory of things. To him the universe is no realization of intelligence, which is to be deciphered by human thought; it is a constitution or system, made up of individual facts, through which we thread our way slowly and inductively. Complete knowledge is impossible; nay, what we call knowledge of any part of the system is inherently imperfect. "We cannot have a thorough knowledge of any part without knowing the whole." So far as experience goes, "to us probability is the very guide of life." Reason is certainly to be accepted; it is pur natural light, and the only faculty whereby we can judge of things. But it gives no completed system of knowledge and in matters of fact affords only probable conclusions. In this emphatic declaration, that knowledge of the course of nature is merely probable, Butler is at one with Hume, who was a most diligent student of the bishop's works. What can come nearer Hume's celebrated maxim - "Anything may be the cause of anything else," than Butler's conclusion, "so that any one thing whatever may, for aught we know to the contrary, be a necessary condition to any other"?
It is this strong grasp or the imperfect character of our knowledge of nature and of the grounds for its limitation that makes Butler so formidable an opponent to his deistical contemporaries. He will permit no anticipations of nature, no a priori construction of experience. "The constitution of nature is as it is," and no system of abstract principles can be allowed to take its place. He is willing with Hume to take the course of experience as the basis of his reasoning, seeing that it is common ground for himself and his antagonists. In one essential respect, however, he goes beyond Hume. The course of nature is for him an unmeaning expression unless it be referred to some author; and he therefore makes extensive use of the teleological method. This position is assumed throughout the treatise, and as against the deists with justice, for their whole argument rested upon the presupposition of the existence of God, the perfect Ruler of the world.
The premises, then, with which Butler starts are the existence of God, the known course of nature, and the necessary limitation of our knowledge. What does he wish to prove? It is not his intention to prove God's perfect moral government over the world or the truth of religion. His work is in no sense a philosophy of religion. His purpose is entirely defensive; he wishes to answer objections that have been brought against religion, and to examine certain difficulties that have been alleged as insuperable. And this is to be effected in the first place by showing that from the obscurities and inexplicabilities we meet with in nature we may reasonably expect to find similar difficulties in the scheme of religion. If difficulties be found in the course and constitution of nature, whose author is admitted to be God, surely the existence of similar difficulties in the plan of religion can be no valid objection against its truth and divine origin. That this is at least in great part Butler's object is plain from the slightest inspection of his work. It has seemed to many to be an unsatisfactory mode of arguing and but a poor defence of religion; and so much the author is willing to allow. But in the general course of his argument a somewhat wider issue appears.