Subject-Verb agreement with compound subjects

[Carol]

Carol earlier:
> 
> FWIW, the whole concept of standard English is not based on
"correctess" (prescriptive grammar) but an agreed upon set of
conventions, similar to those for spelling (which, of course, varies
somewhat depending on whether you're British or American) whose
purpose is to make communication easier. <snip>

Carol again:

Erm, make that "correct*ness*". Unless, of course, correct spelling no
longer matters.

Carol, who will continue to advocate writing in the active voice and
using standard English and avoiding jargon as long as she continues in
her current profession and probably longer