An early classic in comparative philosophy of religion is a 1953 book edited by Charles Hartshorne and William Reese (hereafter: Hartshorne, who was the driving force behind the work) titled Philosophers Speak of God (University of Chicago Press, reissued in 2000 by Humanity Books). This work contains selections from thinkers from around the world and from various traditions on the topic of the concept of God. Extensive introductions to and commentaries on each anthologized author are offered by Hartshorne. These introductions and commentaries are very often worthy contributions in their own right and still deserve attention from philosophers seventy years after initial publication of the book.
One key concept worthy of comparative analysis is “classical theism,” a philosophical (not necessarily scriptural) view of God that has dominated the history of philosophy in Judaism, Christianity, and Islam. This view is monopolar in the sense that God is characterized by being rather than becoming, permanence rather than change, activity rather than passivity, etc. Hartshorne’s stance is that classical theism does a poor job of thinking through the “logic of perfection,” especially regarding intractable problems concerning theodicy (due to a view of God who is assumed to be omnipotent in the sense of being ultimately responsible for everything that occurs) and concerning the incompatibility of belief in human freedom and belief in divine omniscience (in the sense of God knowing with absolute assurance and in minute detail the outcome of future “contingencies”). That is, classical theism collapses in the face of the nastiest version of the problem of evil and the tendency toward determinism. Yet the list of classical theists in the Abrahamic religions is vast: e.g., Philo and Maimonides in Judaism; Saints Augustine, Anselm, Thomas Aquinas, and Descartes in Catholicism, along with many other Christian thinkers like Luther, Calvin, Leibniz, Kant, et al.; and Al-Ghazzali and many others in Islam.
Hartshorne’s preferred alternative to classical theism is called neoclassical (or, more popularly, process) theism, which is dipolar in that there are perfect types of becoming as well as being, change as well as permanence, passivity as well as activity. Further, neoclassical theism includes a critique of divine omnipotence (although God is still seen as ideal power) and a defense of a view of divine omniscience wherein human freedom is preserved. The greatest conceivable being-in-becoming knows all that logically can be known, but no being, not even a divine one, can know the details of the future that are not here yet to be known. This type of theism is also well represented in the Abrahamic religions (even if it is not as pervasive as classical theism), including Jewish thinkers like Martin Buber, Abraham Heschel, and Paul Weiss; many thinkers influenced by Christianity, most notably Henri Bergson, Alfred North Whitehead, Teilhard de Chardin, Nicholas Berdyaev, and Hartshorne himself; and several Muslim thinkers like Mohammed Iqbal. The list of neoclassical theists in all of these religions has grown significantly since the initial publication of Philosophers Speak of God.
There are many other concepts of God in addition to classical theism and neoclassical theism that provide helpful comparative lenses. For example, neoclassical theism was anticipated in the ancient world by Ikhnaton in Egypt, the Judeo-Christian and Hindu scriptures, and Lao-tse, along with Plato, whose later dialogues point toward a concept of God that is difficult to see as compatible with classical theism, despite his (and Aristotle’s) obvious and ironic influence on classical theism. That is, Hartshorne’s analysis of the concept of God is conducive not only to comparative philosophy that is spatially extensive, but also temporally vast. One historical figure who receives special attention is St. Anselm, whose modal version of the ontological argument (discovered by Hartshorne) for the existence of God is defended, but whose classical theistic concept of God is criticized.
Neoclassical theism is also a sort of panentheism (all is in God), in partial contrast to both the otherworldliness of classical theism as well as the strictly immanent God of pantheism (all is God). The latter is represented, e.g., by Asvaghosa and Sankara, as well as by Western thinkers like Spinoza and Josiah Royce. In this regard, neoclassical theism can be seen as a moderate view between classical theism and pantheism. It can also be seen as a moderate stance between strict divine eternity found in classical theism or Plotinian emanationism, on the one hand, and strictly temporalistic theisms that do not include neoclassical divine everlastingness, on the other. Here Hartshorne identifies Samuel Alexander and Henry Nelson Wieman.
The book also has several religious skeptics and atheists represented. But it should not be assumed without argument and without qualification that Buddhism is necessarily a nontheistic religion in that the Buddha himself spoke of an underlying dynamic reality that is unborn, a view that may very well be compatible with certain aspects of neoclassical theism. Here Hartshorne relies on the noted Buddhist scholar D. T. Suzuki.
In short, in this densely argued book there is still much for scholars in comparative philosophy of religion to consider, to mull over, and with which to disagree. It is the sort of book that cannot be read straight through, hence it can understandably be seen as something of a process theistic encyclopedia of comparative religious thought about the concept of God. Further, it offers a way to look at comparative issues that is both thought-provoking and argumentative. It is, of course, a tendentious book, but it is precisely its distinctive point of view that continues to commend itself to us. Hartshorne would have us believe that, in addition to comparing religions, there is also the need to compare concepts of perfection, a logic of perfection that spans across and within religions in unexpected ways.