I think it may be helpful to reconstruct the dialectic between Oppy and Paley to provide some clarity on his objections. Essentially, what Paley (and his contemporary defenders) wants to do is examine the relationship of features that are products of intelligent design within the universe and then make an analogy to try to show that the same reasons that allow us to see that objects within the universe are products of intelligent design, also can carry over when evaluating the universe itself as a whole. Paley wants to say that objects within the universe that have been designed exhibit a certain property (let's call this property X) and that since the universe exhibits the same property, we can say the universe is designed.
Oppy, of course, wants to challenge this reasoning. The first question to ask is regarding the principle source of the inference that we have that the watch is designed; as Oppy puts it, "What is it about watches that makes it 'inevitable' that they should have this effect upon us?" (pg. 32). The answer that Paley gives has to do with the *function* of the watch, as Oppy notes:
"Paley claims that, when we observe the watch, we see that it has a principal function, that its parts have functions, and that the materials from which the watch and its parts are constructed are well suited to the functions that those parts have. Moreover, Paley claims that it is because we see these things that we 'inevitably' form the view that the watch has a maker." (pg. 32)
For Paley, property X is considerations about function, namely that when inspecting objects that have been designed, it is the considerations about an object's function that allow us to discern whether the product is designed or not. However, Oppy contests this and believes there are other considerations at play. Here, I will quote from an earlier work of Oppy's "Arguing About Gods" where he engages in a much more detailed treatment of Paley's argument:
".... there is clearly room for questioning whether Paley has correctly identified the source of our confidence in the 'inference' that a given watch is the product of design. There are at least two difficulties here. On the one hand, it seems highly doubtful that it is considerations about 'function' that play the main role: there are other more immediate things that we see when we inspect the watch that will make the 'inference' to design inevitable. And, on the other hand, it seems highly doubtful that considerations about 'function' could be sufficient to underwrite the 'inference' to design." (pg. 176)
Recall, the main question is, what is property X? Specifically, what is the source of the inference that allows us to see if an object was designed? Paley wants to say that property X is about function. Oppy objects to this in two different ways, by providing a rebutting defeater and an undercutting defeater.
A rebutting defeater offers evidence to show a specific thesis is false. It provides an alternative or more powerful conception of evidence that can rebut the thesis in question and challenge the conclusion.
An undercutting defeater offers reasons for skepticism about the premises or evidence used to support a particular conclusion. It doesn't directly say a specific thesis is false; instead, it provides us good reasons to think that a proponent of an argument has not provided sufficient evidence for the thesis they wish to defend.
Oppy employs both these strategies in his critique of the argument, specifically to show that property X is *not* about function.
Oppy offers an undercutting defeater to show that considerations about function are insufficient to support the inference to design through the discovery of the Antikythera mechanism. In this case, we don't know the function of the object. However, we can still infer design, which can serve as an undercutting defeater to Paley's argument that property is X is about function because we have an argument that challenges the evidence that Paley marshals. To quote Oppy:
"The discoverers of this mechanism immediately recognised that it was a man-made artefact, even though they had no idea about its principal function, nor about the sub-functions served by the parts, nor (consequently) whether the materials from which the mechanism and its parts were constructed were well suited to the functions in question." (pg. 32)
Oppy offers a rebutting defeater to show that the considerations about function don't play the leading role when it comes to the inference that something is designed by providing an alternative account, namely considerations about a thing's background knowledge having a more immediate role in allowing us to see whether an object is designed or not. As noted earlier, it has to do with considerations related to our background knowledge of the objects and materials in question:
"Well, they could see immediately that it was composed from metals that do not occur in nature – for example, bronze. They could see immediately that it has a shape that does not belong to the natural world. They could see immediately that there were cog-wheels in its interior – and, of course, they knew full well that cog-wheels do not grow on trees. Etc." (pg. 33)
Oppy elaborates on this in "Arguing About Gods":
"The compelling reasons that we have for supposing that the watch is the product of intelligent design simply do not carry over to reasons for supposing that the natural world is the product of intelligent design. The background knowledge that we have about the production of manufactured materials and components is not paralleled by any comparable knowledge about the production of biological materials and components." (pg. 177)
Both of these objections offer some decisive reasons for thinking that Paley's argument doesn't go through. While they may seem contradictory on the surface, when we understand the dialectical context and the nature of the objections being offered, it is much easier to see how they can serve as powerful rebuttals to the argument. Oppy challenges the evidence that Paley supports in consideration for his inference to design but also provides an alternative conception of the inference that isn't based on function.
With this clarity in mind, I think when you summarize Oppy's objections as follows:
"Because we can easily discern that the watch is a man-made artifact, all the argument proves, according to Oppy, is that we can recognize "artifacts" as obvious. It does not prove that God makes artifacts so that we can know God exists. Additionally, he says, there is a natural explanation for design in nature. Evolutionary theory can explain the presence of the complexity of living systems, living things, and the organization of organs, tissues, and cells. Evolution does not produce things like the Antikythera mechanism."
I would point out that it doesn't have to do with recognizing artifacts simpliciter, but rather more so because of our background knowledge of the materials and entities in question, which I think can address some of your points about artifacts on Naturalism.
I think most atheists would be happy to admit that human artifacts are "natural" in the broadest possible sense you're describing here - human agents are still the result of natural processes, and I personally see it as a good thing that naturalism weakens any intrinsic division you might make between them. We *shouldn't* think of the things we produce as entirely different from the things bees produce, or even the things plants or glaciers produce. But it still seems as though we can make meaningful distinctions between agential causes and non-agential causes in the meantime. As an atheist, I would just say an artifact is (roughly) anything produced by the intentional effort of a rational agent. The fact the the rational agent is themselves a product of an irrational natural process doesn't seem to cause any particular issue metaphysically. As an analogy, I might say that a particular compound is anything produced by a particular chemical reaction - the fact that the elements involved in that reaction are not themselves the product of the same chemical reaction isn't an issue, right?
I think it may be helpful to reconstruct the dialectic between Oppy and Paley to provide some clarity on his objections. Essentially, what Paley (and his contemporary defenders) wants to do is examine the relationship of features that are products of intelligent design within the universe and then make an analogy to try to show that the same reasons that allow us to see that objects within the universe are products of intelligent design, also can carry over when evaluating the universe itself as a whole. Paley wants to say that objects within the universe that have been designed exhibit a certain property (let's call this property X) and that since the universe exhibits the same property, we can say the universe is designed.
Oppy, of course, wants to challenge this reasoning. The first question to ask is regarding the principle source of the inference that we have that the watch is designed; as Oppy puts it, "What is it about watches that makes it 'inevitable' that they should have this effect upon us?" (pg. 32). The answer that Paley gives has to do with the *function* of the watch, as Oppy notes:
"Paley claims that, when we observe the watch, we see that it has a principal function, that its parts have functions, and that the materials from which the watch and its parts are constructed are well suited to the functions that those parts have. Moreover, Paley claims that it is because we see these things that we 'inevitably' form the view that the watch has a maker." (pg. 32)
For Paley, property X is considerations about function, namely that when inspecting objects that have been designed, it is the considerations about an object's function that allow us to discern whether the product is designed or not. However, Oppy contests this and believes there are other considerations at play. Here, I will quote from an earlier work of Oppy's "Arguing About Gods" where he engages in a much more detailed treatment of Paley's argument:
".... there is clearly room for questioning whether Paley has correctly identified the source of our confidence in the 'inference' that a given watch is the product of design. There are at least two difficulties here. On the one hand, it seems highly doubtful that it is considerations about 'function' that play the main role: there are other more immediate things that we see when we inspect the watch that will make the 'inference' to design inevitable. And, on the other hand, it seems highly doubtful that considerations about 'function' could be sufficient to underwrite the 'inference' to design." (pg. 176)
https://philpapers.org/rec/OPPAAG-2
Recall, the main question is, what is property X? Specifically, what is the source of the inference that allows us to see if an object was designed? Paley wants to say that property X is about function. Oppy objects to this in two different ways, by providing a rebutting defeater and an undercutting defeater.
A rebutting defeater offers evidence to show a specific thesis is false. It provides an alternative or more powerful conception of evidence that can rebut the thesis in question and challenge the conclusion.
An undercutting defeater offers reasons for skepticism about the premises or evidence used to support a particular conclusion. It doesn't directly say a specific thesis is false; instead, it provides us good reasons to think that a proponent of an argument has not provided sufficient evidence for the thesis they wish to defend.
Oppy employs both these strategies in his critique of the argument, specifically to show that property X is *not* about function.
Oppy offers an undercutting defeater to show that considerations about function are insufficient to support the inference to design through the discovery of the Antikythera mechanism. In this case, we don't know the function of the object. However, we can still infer design, which can serve as an undercutting defeater to Paley's argument that property is X is about function because we have an argument that challenges the evidence that Paley marshals. To quote Oppy:
"The discoverers of this mechanism immediately recognised that it was a man-made artefact, even though they had no idea about its principal function, nor about the sub-functions served by the parts, nor (consequently) whether the materials from which the mechanism and its parts were constructed were well suited to the functions in question." (pg. 32)
Oppy offers a rebutting defeater to show that the considerations about function don't play the leading role when it comes to the inference that something is designed by providing an alternative account, namely considerations about a thing's background knowledge having a more immediate role in allowing us to see whether an object is designed or not. As noted earlier, it has to do with considerations related to our background knowledge of the objects and materials in question:
"Well, they could see immediately that it was composed from metals that do not occur in nature – for example, bronze. They could see immediately that it has a shape that does not belong to the natural world. They could see immediately that there were cog-wheels in its interior – and, of course, they knew full well that cog-wheels do not grow on trees. Etc." (pg. 33)
Oppy elaborates on this in "Arguing About Gods":
"The compelling reasons that we have for supposing that the watch is the product of intelligent design simply do not carry over to reasons for supposing that the natural world is the product of intelligent design. The background knowledge that we have about the production of manufactured materials and components is not paralleled by any comparable knowledge about the production of biological materials and components." (pg. 177)
Both of these objections offer some decisive reasons for thinking that Paley's argument doesn't go through. While they may seem contradictory on the surface, when we understand the dialectical context and the nature of the objections being offered, it is much easier to see how they can serve as powerful rebuttals to the argument. Oppy challenges the evidence that Paley supports in consideration for his inference to design but also provides an alternative conception of the inference that isn't based on function.
With this clarity in mind, I think when you summarize Oppy's objections as follows:
"Because we can easily discern that the watch is a man-made artifact, all the argument proves, according to Oppy, is that we can recognize "artifacts" as obvious. It does not prove that God makes artifacts so that we can know God exists. Additionally, he says, there is a natural explanation for design in nature. Evolutionary theory can explain the presence of the complexity of living systems, living things, and the organization of organs, tissues, and cells. Evolution does not produce things like the Antikythera mechanism."
I would point out that it doesn't have to do with recognizing artifacts simpliciter, but rather more so because of our background knowledge of the materials and entities in question, which I think can address some of your points about artifacts on Naturalism.
I think most atheists would be happy to admit that human artifacts are "natural" in the broadest possible sense you're describing here - human agents are still the result of natural processes, and I personally see it as a good thing that naturalism weakens any intrinsic division you might make between them. We *shouldn't* think of the things we produce as entirely different from the things bees produce, or even the things plants or glaciers produce. But it still seems as though we can make meaningful distinctions between agential causes and non-agential causes in the meantime. As an atheist, I would just say an artifact is (roughly) anything produced by the intentional effort of a rational agent. The fact the the rational agent is themselves a product of an irrational natural process doesn't seem to cause any particular issue metaphysically. As an analogy, I might say that a particular compound is anything produced by a particular chemical reaction - the fact that the elements involved in that reaction are not themselves the product of the same chemical reaction isn't an issue, right?