Ever since the Great Multimethod Debate, I've been introducing various principles into my arguments. These are my "axioms of semantics", and my hope is to take the hard questions and answer them purely in terms of reasoning from these basic principles. This is the kind of reasoning that makes me love mathematics: to reduce all hard decisions into obvious truths by using proper definitions of terms.
So, anyway, here's the list I have so far. (The other well-known Perl principles like Least Surprise, Waterbed, and Endweight are omitted. Maybe I'll do a writeup about those soon.)
The motivations for the three were: manhattan MMD, the junctive one() type, and manhattan MMD again, respectively. Also note that the first principle precludes the existence of submethods. Now it's clear why I keep asking why we need submethods. It's not entirely clear why I continue not to get any answers.
 Up to metainformation, such as asking which class the object is in, of course.
 To be fair, Damian responded to my query, but he didn't answer my question. He gave more an example of how submethods are used, rather than why they are used.