ABSTRACT
In Part IX of Dialogues Concerning Natural Religion, Demea presents “that simple and sublime argument a priori” for the existence of God, a version of the cosmological argument. Scholars have generally identified Samuel Clarke's demonstration as Hume's likely historical source. However, Clarke is an awkward target, because Cleanthes's criticisms are drawn from Hume's empiricist principles, which Clarke would reject. I discuss Demea's demonstration in light of the demonstration offered by John Locke in An Essay Concerning Human Understanding Book 4, Chapter 10. I distinguish three causal principles that Locke's demonstration uses and analyze his proofs of them. For Locke, “necessary existence” is not a positive idea distinct from the idea of existence; instead, it refers to the demonstrable necessary connection between the ideas of my existence and the existence of God. Cleanthes's “decisive” argument against Demea's argument rests on the claim that matters of fact cannot be demonstrated. This parallels criticisms from A Treatise of Human Nature that Hume makes of Locke's putative demonstration of the causal principle, “whatever begins to exist, must have a cause of existence” (THN I.iii.3.1). If this causal principle cannot be demonstrated, Locke has not proven that God necessarily exists. Philo's further criticism that Demea's argument fails to produce religious belief for many people is especially salient against Locke, because it echoes a similar criticism Locke made against Descartes's ontological argument.
