Joined: Mar. 2005
I did not mean to imply that I would go about a discussion of nested hierarchies in the same way. As no predictions follow from a designer, no predictions about nested hierarchies follow from a designer. Thus, the conclusion I reached concerning the unity of life can be generalized to cover the other predictions of common descent.
I wanted to discuss this statement of yours:
|(2) is out because it is a distinction without a difference. ...Whether one chooses to use "prediction" or "consistency with the available evidence" is pure semantics. There are possible states of the evidence that common descent would not be able to accommodate.|
I think the distinction presents a difference. Common descent is the theoretical claim (sentence) that "all known biota are descended from a single common ancestor." A prediction of common descent is an observation claim (cf. Quine's observation sentence) that is logically deduced from the theoretical claim, e.g., "cladistic analyses of organisms produce phylogenies that have large, statistically significant values of hierarchical structure."
A prediction is a logical implication of the theoretical claim. Accordingly, the theory can be falsified using a modus tollens:
If [theoretical claim] then [observation claim]
Not [observation claim]
Therefore, not [theoretical claim]
That is, if the observation claim is false, the theory is false.
On the other hand, an observation claim is merely consistent with a theoretical claim if both can be true together, but the falsity of the observation claim does not imply the falsity of the theoretical claim. Statements that are merely consistent with a theoretical claim cannot be deduced from that theoretical claim. For example, observation claims concerning the unity of life are consistent with my previous theoretical claim that "all known biota are special creations of a single designer," i.e., they can both be true together, but the latter does not follow logically from the former, and its falsity does not result in the falsity of the thoeretical claim.
My question, then, is whether the observation claim that "cladistic analyses of organisms produce phylogenies that have large, statistically significant values of hierarchical structure" is a prediction of common descent or whether it is merely consistent with common descent? Is there a conceivable scenario in which common descent would be true and the observation claim false? If there were, the observation claim could not be a deduction from from the theoretical claim, and therefore, it could not be a prediction.