Enlightenment thinking on religion culminated in the late 18th century in the work of the German philosopher Immanuel Kant. Kant argued that time, space, causation, and substance—among other features of reality—are innate conceptual categories through which the human mind imposes order on experience. There can be no knowledge of matters allegedly existing beyond these categories; thus, there can be no knowledge of God and, hence, no theological knowledge. Having thus written off any metaphysical justification of religion, Kant introduced a conception of religion that arose from his idea of morality. Morally right acts, he held, are those aimed at bringing about the highest good (summum bonum), a state in which people are rewarded with happiness in proportion to the level of virtue they achieve. But one cannot rationally will to bring about the highest good unless one believes that such a state is possible, and it is possible only in an eternal afterlife ordered by God. The existence of God and the immortality of the soul can thus be “postulated” as rational conditions of morality, even though they cannot be proved theoretically. In this way religion, for Kant, was a matter of practical reason, concerned with what people ought to do, rather than of theoretical reason, concerned with what people have good reason to think is true (see below Religion and morality).
Immanuel Kant, print published in London, 1812.Photos.com/Jupiterimages
Philosophy of religion since the 19th century
It is a short but significant step from postulating the existence of God as a condition of morality to regarding the idea of God as a “projection” of human concerns. It is a step that a number of thinkers after Kant—including the German philosopher Ludwig Feuerbach and the Austrian founder of psychoanalysis Sigmund Freud—readily took. They saw religion as compensation for, and therefore an escape from, unhappy aspects of the human condition. A notable and influential example of this approach is that of Karl Marx, who saw religion as “the sigh of the oppressed creature, the heart of a heartless world and the soul of soulless conditions. It is the opium of the people.” Along with those who viewed the idea of God as projection were thinkers, sometimes under the influence of modern science, who neither accepted nor rejected God’s existence. The English biologist Thomas Henry Huxley coined the term agnosticism as a name for the view that there is no conclusive evidence for or against the existence of God. However, many scientists, like the American botanist Asa Gray, sought ways of harmonizing scientific advances with orthodox Christianity.
Forms of religion based on idealism (a philosophical movement that stressed the spiritual or ideational in the interpretation of experience) abandoned the idea of a transcendent God and identified the divine with wholly immanent attitudes or processes. Friedrich Schleiermacher, for example, saw religion as the feeling of absolute dependence or the recognition of contingency, while G.W.F. Hegel, the greatest of the idealists, identified true religion with the development of the entire world order. Not only is God in history; God is history. These views, often raised against mechanistic and utilitarian attitudes in the 19th century, were attractive because of the vague religiosity, sometimes of a pantheistic character, that they encouraged.
During the 20th century philosophical interests were secularized, with the consequence that the strong link between mainstream philosophy and the discussion of religious questions was weakened. In the 1920s and ’30s the logical positivists, and later the noncognitivists, declared that metaphysical and theological (as well as ethical and aesthetic) sentences are literally meaningless because they cannot be verified through sense experience. Sentences about the qualities of God or about the nature of spiritual experience, for example, make claims about entities or events that cannot be empirically observed or demonstrated. Thus, sentences such as “God is love” and “divine grace works upon the soul” are empty of cognitive content and therefore neither true nor false.
The widespread abandonment of logical positivism in the 1950s and ’60s (due in part to its inability to account for the meaningfulness of certain scientific propositions and counterfactual truths), led to a revival of traditional metaphysics and a consequent resurgence of interest in themes in the philosophy of religion that had engaged thinkers before Kant, such as Gottfried Wilhelm Leibniz (1646–1716). As a result, contemporary philosophy of religion, certainly in the English-speaking world, has much more in common with medieval philosophy than it does with the philosophy of the 19th century. Continental (German and French) philosophy of religion, however, continues to be rooted in the more iconoclastic tradition of Feuerbach and Freud. Main philosophical themes
The main themes that arise in the philosophy of religion have been shaped by issues concerning the relation between human language and thought on the one hand and the nature of the divine on the other. If it is possible neither to think nor to speak about God, then it is obviously impossible to argue philosophically about him. The difficulties can be seen by considering some extreme positions. If language about God or the divine is totally equivocal, then saying that God is good or claiming to know that God is good bears no relation whatever to standards of human goodness. If language about God is wholly anthropomorphic, then God is reduced to human proportions, eliminating any transcendent reference. Yet if God is utterly transcendent, it is doubtful that humans could possess an adequate concept of him or form true propositions about him.
While philosophers have varied a great deal in their accounts of language about God (though all acknowledge the use of metaphors and models in conveying understanding), they have generally recognized that some element of univocity is indispensable if there are to be credible claims to reason about God’s reality. It is sometimes argued that such language is best expressed in negative terms: God is infinite (not finite), timeless (not in time), and so on. Epistemological issues
The main epistemological question in the philosophy of religion is: Can God be known? This apparently simple question quickly leads to issues of considerable complexity. There are two main areas of debate: (1) whether it is possible to prove the existence of God—and, if not, whether there is nevertheless a sense in which religious belief is reasonable—and (2) whether knowledge of God is obtainable from sources other than human reason and sense experience.
Proofs of the existence of God are usually classified as either a priori or a posteriori—that is, based on the idea of God itself or based on experience. An example of the latter is the cosmological argument, which appeals to the notion of causation to conclude either that there is a first cause or that there is a necessary being from whom all contingent beings derive their existence. Other versions of this approach include the appeal to contingency—to the fact that whatever exists might not have existed and therefore calls for explanation—and the appeal to the principle of sufficient reason, which claims that for anything that exists there must be a sufficient reason why it exists. The arguments by Aquinas known as the Five Ways—the argument from motion, from efficient causation, from contingency, from degrees of perfection, and from final causes or ends in nature—are generally regarded as cosmological. Something must be the first or prime mover, the first efficient cause, the necessary ground of contingent beings, the supreme perfection that imperfect beings approach, and the intelligent guide of natural things toward their ends. This, Aquinas said, is God. The most common criticism of the cosmological argument has been that the phenomenon that God’s existence purportedly accounts for does not in fact need to be explained.