Re: Strange thoughts on PN - was Re: BAD vs. BADD

[Nick Pharris <npharris@umich.edu>]

Quoting Martin Baeker <martin.baeker@tu-bs.de>:


> Everybody here agrees that group A=(Megalos.+Iguanodon) is useful, as
> is B=(Passer+Archaeopteryx) - where () denotes MRCA - despite the fact
> that these are also quite arbitrary - there will be a critter looking
> *almost* like the first member of A that is not a member of it (like
> Lagosuchus), but still, the concepts are useful, albeit arbitrary.
>
> Why is then A\B (A without-B) such a big no-no?

Ah, but you've just answered your own question.  If B is treated as a 
subgroup of A, then we can recognize groups like (B+_Deinonychus_), to 
include B and "critters that look *almost* like the first member of B 
but are not members of B".

However, if A and B are recognized as separate and coequal groups, then 
we do not have this option, unless we want to have a highly confusing 
system of overlapping groups.

--
Nick Pharris
Department of Linguistics
University of Michigan

"Creativity is the sudden cessation of stupidity."
    --Edwin H. Land