David Hume (1711-1776) generally regarded as the most important philosopher ever to write in English -- the last of the great triumvirate of "British empiricists" -- was also noted as an historian and essayist. A master stylist in any genre, Hume's major philosophical works -- A Treatise of Human Nature (1739-1740), the Enquiries concerning Human Understanding (1748) and Concerning the Principles of Morals (1751), as well as the posthumously published Dialogues concerning Natural Religion (1779) -- remain widely and deeply influential, despite their being denounced by many of his contemporaries as works of scepticism and atheism. While Hume's influence is evident in the moral philosophy and economic writings of his close friend Adam Smith, he also awakened Immanuel Kant from his "dogmatic slumbers" and "caused the scales to fall" from Jeremy Bentham's eyes. Charles Darwin counted Hume as a central influence, as did "Darwin's bulldog," Thomas Henry Huxley. The diverse directions in which these writers took what they gleaned from reading Hume reflect not only the richness of their sources but also the wide range of Hume's empiricism. Comtemporary philosophers recognize Hume as one of the most thoroughgoing exponents of philosophical naturalism. 
The design argument
One of the oldest and most popular arguments for the existence of God is the design argument that all the order and 'purpose' in the world bespeaks a divine origin. A modern manifestation of this belief is creationism. Hume gave the classic criticism of the design argument in Dialogues Concerning Natural Religion and An Enquiry Concerning Human Understanding and though the issue is far from dead in modern debate, many are convinced that Hume killed the argument for good. Here are some of his points:
- For the design argument to be feasible, it must be true that order and purpose are observed only when they result from design. But order is observed regularly, resulting from presumably mindless processes like snowflake or crystal generation. Design accounts for only a tiny part of our experience with order and 'purpose'.
- Furthermore, the design argument is based on an incomplete analogy: because of our experience with objects, we can recognise human-designed ones, comparing for example a pile of stones and a brick wall. But in order to point to a designed Universe, we would need to have an experience of a range of different universes. As we only experience one, the analogy cannot be applied.
- Even if the design argument is completely successful, it could not (in and of itself) establish a robust theism; one could easily reach the conclusion that the universe's configuration is the result of some morally ambiguous, possibly unintelligent agent or agents whose method bears only a remote similarity to human design.
- If a well-ordered natural world requires a special designer, then God's mind (being so well-ordered) also requires a special designer. And then this designer would likewise need a designer, and so on ad infinitum. We could respond by resting content with an inexplicably self-ordered divine mind; but then why not rest content with an inexplicably self-ordered natural world?
- Often, what appears to be purpose, where it looks like object X has feature F in order to secure some outcome O, is better explained by a filtering process: that is, object X wouldn't be around did it not possess feature F, and outcome O is only interesting to us as a human projection of goals onto nature. This mechanical explanation of teleology anticipated natural selection. (see also Anthropic principle)