Quote:
Originally Posted by NotReady
From Wiki:
The teleological argument is logically valid if the premises are true - the conclusion MUST be true if it follows from the premises, but if one or more premises is false, then the argument is unsound, even though valid.
Again, from Wiki, a modified simple formulation, not necessarily how I would state it, but for example:
1. Complexity is impossible without a designer.
2. The universe is highly complex.
3. Therefore, the universe has a designer.
If 1 and 2 are true, 3 MUST be true. You can attack 1 and 2, but you are wrong if you think 3 is logically invalid.
This is a minor point and not really relevant to our discussion. But I'll try to explain. I don't understand what you were trying to say in your first paragraph, so I'll just briefly clarify what logicians mean by "validity." When I say an argument is valid, what I mean is that if the premises are true, then the conclusion must be true. Or, an argument is valid if it is impossible for the premises to be true and the conclusion false.
The reason why I say that analogical arguments are invalid is that the epistemic warrant they provide does not come from the validity of the argument form. You'll note that the general form of analogical arguments I provided above is an invalid argument form. But that is fine. Not all good arguments are valid--only good deductive arguments. The justification provided by analogical arguments comes from some other principle of reason--exactly what is controversial, but not from the argument form itself.
So, looking at your example. Here's a cleaned up version.
1. All complex objects have a designer.
2. The universe is a complex object.
3. The universe has a designer.
This is a valid argument. The problem is that it isn't the design argument. Rather it
assumes the design argument in the first premise. Pretty much everyone agrees with (2). So for this argument to be successful, we must have good reason to accept (1). What is this reason? And here is where we get an analogy between complex objects like watches or cars and complex objects like eyes and galaxies.
Putting this into argument form:
4. Eyes and watches both have ordered complexity.
5. Watches were made by an intelligent being.
6. Therefore, eyes were [probably] made by an intelligent being.
As you can see, this argument is not valid. Might be a good argument still, but on different grounds than deductive force.
Or another example:
7. All complex objects we've seen created were made by an intelligent being.
8. Therefore, all complex object are created by an intelligent being.
Again, this is an invalid argument--but that doesn't make it a bad argument (though it is not an analogical argument). Why? It is the old black swan story. People used to say that all swans observed are white, therefore, all swans are white. Nothing wrong with that as an inference. However, it is of course true that there could be non-white swans that have just not yet been observed (as ending up being the case). Thus, even though inductive arguments of this sort can be very powerful, it is possible for the premises to be true and the conclusion false and so it is an invalid argument form. Of course, this is all a bit misleading--we shouldn't even be discussing the validity of inductive arguments as validity only applies to deductive arguments.
Final point, and here I'm really being particular, you say that (3) is logically valid. But validity is a property of arguments, not statements, and so it doesn't make sense to claim that a statement is logically valid.