You've then simply declared that the two subsets must share all properties - if one subset is designed then so must the other subset be, but you haven't provided any logic as to why that should be the case. — Pseudonym
The logic (the inference) is very simple, straight forward, and compelling, which is why most people believe it's true. The point is that when we look at human productions that exhibit the features named in premise one,
they are the result of intelligent design. In fact, even if you had never seen a watch before (Paley's argument), and stumbled upon one, you surely wouldn't conclude it happened by chance. Why? Because we are very familiar with the evidence of intelligent design. Again, the evidence that is spelled out in premise one. Moreover, it's not just how complex the item is, it can be very simple or very complex, but all, or nearly all manmade productions have this property (as stated in premise one).
Now the argument is analogical, that is, we make an inference based on a likeness or analogy between objects or groups of objects to infer the existence of a further likeness. This kind of reasoning is done all the time in logic, so to say that there is no logic to the argument, is to
not understand logic.
All we know about these two subsets, is that they must share at least and only the one property that makes them both part of the same set i.e that the parts are so arranged that the completed whole is able to achieve or be used to achieve activities of a higher order than any part alone. There's no reason, inductive or otherwise, to presume that they will share any other properties, such as being designed. — Pseudonym
We will concentrate on the last sentence of this paragraph, which misses the point of the argument. The property as put forth in premise one,
is the evidence of intelligent design. Thus, if it is the evidence of intelligent design, then it follows with certainty, that is, with a high degree of probability that other artifacts exhibiting these same features are also intelligently designed.
The logic is there, and only those who are committed to a dogmatic world view refuse to see the evidence. This is why I say these kinds of naturalistic world views, are just as bad as religious dogmatism.
Again, the argument is inductive, and clearly inductive. Anyone who has had even a basic course in logic can see this.
Let's analyze the strength of the argument:
1) Number of items used as evidence, and the number of items used as evidence are human artifacts and objects of nature; they are innumerable.
2) The number of analogies (similarities) shared by the objects compared. Virtually all of the objects are complex consisting of many parts, some are more complex than others. Moreover, the parts fits with some degree of precision.
3) Number of disanalogies (dissimilarities) between human artifacts and natural artifacts. "I do not know of any disanalogies between all human productions, on the one hand, and all objects of nature, on the other. Some objects of nature are alive, but not all are. Some have a mental life, but not all. Similarly, some human productions are also alive, as in the case of genetically engineered plants and animals."
4) Variety of items used as evidence, namely human productions. The variety is endless.
5) The issue of relevance of the features or structures compared, namely the parts are so arranged that the whole can perform higher functions than any part alone, to the activity of design. Does design cause such structure? The relevance, of course, is perfect, for what is the activity of design but the arrangement of parts so the whole can perform a higher function than any part alone?
6) Scope of the conclusion - the conclusion is the narrowest and most conservative possible, namely, that there are one or more designers of natural objects.
7) Truth and cogency of the premises, i.e., knowledge of the truth of the premises. Nearly every human adult knows the premises are true.
8) Cogency of the argument structure. Can the argument be followed? The argument is very simple and easy to follow.
9) Psychological impact or compellingness of the argument. My experience is that most find it compelling; only committed agnostics and atheists do not, and they are few and far between. They just refuse to draw the proper conclusion
The result of the analysis is that the argument is a very strong argument. It is hard to imagine a stronger argument than this. It is probably one of the reasons why so many people believe the argument. The only way to get around the strength of this argument is to keep repeating "There is no evidence." You say it enough times, then others will repeat it and believe it. Reminds of politics, the politicians know if they keep repeating a narrative, a certain segment of the population will believe it. And the narrative that atheists and agnostics (by the way I'm an agnostic) keep repeating, is, "There is no evidence.," among other insulting remarks.
I will set forth the challenge once again. If their rejection of the argument (mostly atheists and agnostics) isn't based on a prejudice apart from the evidence, then they should be able to stipulate what additional evidence would count as evidence of intelligent design in the universe. In other words, what evidence is lacking that would warrant believing in an intelligent designer/s?
If they cannot stipulate what is lacking, then their belief is an irrational prejudice sealed off from the evidence. They would be committing the fallacy of the self-sealing argument.
And if nothing would count as evidence of intelligent design, then their argument is unfalsifiable.
It's not that difficult to argue intelligent design. In fact, it's very easy to defeat the counter-arguments, and there is no need to argue against evolution. The problem is that many people are afraid to argue these points, especially in a university setting, because they get laughed at by those who have swallowed hook, line, and sinker a particular world view. Let them laugh, they're the ones being irrational.