Within philosophy of religion, a cosmological argument is understood to be an argument from the existence of the world to the existence of God. Typically, such arguments proceed in two steps. The fi rst step argues from the existence of the world to the existence of a fi rst cause or necessary being that accounts for the existence of the world (see Chapter 33 , Necessity). The second step argues that such a fi rst cause or necessary being has, or would very likely have, the properties associated with the idea of God. Cosmological arguments appeared in Plato and Aristotle, played a prominent role in Jewish, Christian, and Islamic thought during the medieval period, and were forcefully presented in the eighteenth century by Gottfried Leibniz and Samuel Clarke. In the modern period these arguments, particularly as presented by Thomas Aquinas, Leibniz, and Clarke, have been severely criticized by David Hume, Immanuel Kant, and others. In the last few decades of the twentieth century, however, there was a revival of interest in cosmological arguments, and several challenges to the major criticisms of these arguments have appeared.
Cosmological arguments may be divided into two broad types: those that depend on a premise denying an infi nite regress of causes and those that do not depend on such a premise. Among the former are contained the fi rst " three ways " presented by Aquinas, as well as an interesting argument, developed by Islamic thinkers, that the world cannot be infi nitely old and, therefore, must have come into existence by the creative will of God (see Chapter 9 , The Christian Contribution to Medieval Philosophical Theology; and Chapter 10 , The Islamic Contribution to Medieval Philosophical Theology). An important difference between the arguments represented by Aquinas ' s fi rst " three ways " and the Islamic argument is that while both reject an infi nite regress of causes, only the latter bases the objection on the alleged impossibility of an infi nite temporal regress. Unlike Bonaventure, who adopted the Islamic argument, Aquinas did not think that philosophy could show that the world had a temporal beginning. He rejected an infi nite regress of essentially ordered causes (a non -temporal causal series), identifying God as the fi rst cause in such a non -temporal series. Leibniz and Clarke, however, allowed an infi nite regress of causes, arguing only that there must be a suffi cient reason for the existence of such a series of causes. Thus the eighteenth -century arguments of Clarke and Leibniz do not depend on rejecting an infi nite regress of causes. Appealing to the principle of suffi cient reason, Clarke and Leibniz insist only that such a series could not be self -explanatory and, therefore, would require an explanation in A Companion to Philosophy of Religion, Second Edition Edited by C. Taliaferro, P. Draper and P. L. Quinn