One of the oldest and most popular arguments for the existence of God is the design argument: that order and “purpose” in the world bespeaks a divine origin.
Hume gave a criticism of the design argument in Dialogues Concerning Natural Religion and An Enquiry Concerning Human Understanding.
Firstly, Hume argued that 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 often observed to result from presumably mindless processes like the generation of snowflakes and crystals. Design can account for only a tiny part of our experience of order.
Second, that the design argument is based on an incomplete analogy: because of our experience with objects, we can recognize 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.
Next, 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.
Furthermore, 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?
Finally, Hume advanced a version of the Anthropic Principle. Often, when it appears that an object has a particular feature in order to secure some goal, it is in fact the result of a filtering process. That is, the object wouldn’t be around did it not possess that feature, and the perceived purpose is only interesting to us as a human projection of goals onto nature. This mechanical explanation of teleology anticipated the notion of natural selection.
In astrophysics and cosmology, the anthropic principle (from Greek anthropos, meaning “human”) is the philosophical consideration that observations of the physical Universe
must be compatible with the conscious and sapient life that observes it. Some proponents of the anthropic principle reason that it explains why the Universe has the age and the fundamental physical constants necessary to accommodate conscious life. As a result, they believe it is unremarkable that the universe’s fundamental constants happen to fall within the narrow range thought to be compatible with life.
The strong anthropic principle (SAP) as explained by Barrow and Tipler (see variants) states that this is all the case because the Universe is compelled, in some sense, to eventually have conscious and sapient life emerge within it. Critics of the SAP argue in favor of a weak anthropic principle (WAP) similar to the one defined by Brandon Carter, which states that the universe’s ostensible fine tuning is the result of selection bias: i.e., only in a universe capable of eventually supporting life will there be living beings capable of observing and reflecting upon any such fine tuning, while a universe less compatible with life will go unbeheld. Most often such arguments draw upon some notion of the multiverse for there to be a statistical population of universes to select from and from which selection bias (our observance of only this Universe, apparently compatible with life) could occur.