 Metaphysicians have wanted to account for the very existence, or nature, of some things by appealing to things on which they ontologically depend: for example, a complex object exists and is the way it is because its parts exist and are the way they are; a set exists because its members exist; etc. (See Fine 1995 and Koslicki 2013 for discussion.) But of course the things the dependent beings depend on must themselves exist as well. Some have been suspicious of the idea that this can go on ad infinitum, with every thing being ontologically dependent on some new thing(s), and thus have argued for Metaphysical Foundationalism: the view that there is a collection of absolutely  fundamental[4]  entities upon which all else ultimately ontologically depends. Aquinas, e.g., holds that events are ontologically dependent on their causes, and that an infinite regress of causes and effects would be an infinite series of things each of which is ontologically dependent on the next, and this is  impossible.[5]  Thus he concludes that there must be a first cause of all else that is itself uncaused—namely, God. We shall see more examples of Metaphysical Foundationalists below. See also the supplementary document on