I. The Classical (“Old School”) Design Argument
A. An argument from analogy (between human artifacts and natural objects)
1. The argument points out that human artifacts and living organisms/their parts are analogous/similar in a number of respects:
a. both are complex (i.e., have parts)
b. the parts of both work together to perform a function
2. It then concludes that since both are similar in these respects, and since human artifacts are intelligently designed, the latter are probably intelligently designed as well
B. It thus typically appeals to biological organisms and their parts as instances of apparent design
C. Four main criticisms
1. The “Weak Analogy” objection: the analogy between human artifacts and biological organisms (and their parts) is too weak to confidently infer that the latter were intelligently designed
2. The “Design Mimickers” objection: it seems as though other, non-intelligent causes can mimic the effects of designers (i.e., complex, functional things)
a. We see in nature that there are also many non-intelligent causes of complex, functional things (e.g., spiders produce spider webs by instinct; tiny seeds contain an internal principle of order that lead to various kinds of vegetation (e.g., plants, trees, vegetables), etc.).
b. Neo-Darwinian evolution can produce the complex, functional structures seen in living things
3. The “Who Designed the Designer?” objection:
a. Either all complex, functional things require an intelligent designer, or some don’t
b. If all entities that have parts that work together to perform a function require an intelligent designer, then since the mind of the hypothetical designer of the natural world seems to bear these traits, then it, too, would need a designer.
c. On the other hand, if some entities with these features don’t require an intelligent designer (e.g., God), then why can’t we say that same thing about living organisms, or at least the universe?
d. Therefore, either God needs an intelligent designer, or we have no good reason to think that living organisms – or at least the universe – needs an intelligent designer
e. The basic point here is that *both* key hypotheses -- theism and naturalism -- have brute functional complexity (i.e., functional complexity that has no prior cause), and so it's special pleading to say that one sort of complexity requires an explanation while the other does not.
4. The “Even if it Worked” Objection: Even if the argument works, it doesn’t prove that the designer is the god of theism. I.e., it wouldn’t prove that:
a. the designer is all-knowing
b. the designer is all-powerful
c. the designer is perfectly good
d. the designer is an immaterial spirit
e. the designer is eternal
f. the designer is omnipresent (present everywhere)
g. the designer is also the creator
h. there is just one designer
i. the designer still exists
II. The Contemporary (“New School”) Design Argument
A. An Inference to the Best Explanation (theory that best explains certain data)
1. It’s not an argument from analogy
2. It therefore avoids the “weak analogy” objection
B. Typically appeals to non-biological natural objects as instances of apparent design – esp. the fine-tuning of the cosmos
1. It therefore allows that living organisms arose by evolution
2. It therefore avoids the “evolution” objection
C. The main criticism: The “Many Universes” objection
1. The hypothesis of a multiverse – i.e., the hypothesis that there are lots and lots of other universes, each having different numerical values for its fundamental constants – seems to explain the data of the fine-tuning of the cosmos just as well as the “intelligent designer” hypothesis.
2. The “Design Mimicker” objection thus seems to arise in the non-biological realm as well.
III. The key response from the theist:
A. These criticisms may show that the design argument fails to make the theistic hypothesis more probable than not (i.e., of a probability above .5). However, that doesn't entail that the design argument fails to raise the probability of theism at least somewhat (to pick an aribitrary number, say .3)
B. However, when the design argument is combined with other arguments – the cosmological argument, the argument from religious experience, etc. – then there is a good cumulative case for theism.