Here's a rule - The Comma Splice;
To use one is a dreadful vice.
Some other method must be found
or one's grammar will be deemed unsound.
Yet we shouldn't pick on those who famous
use it lest our ignorance shame us.
Apparently it's ok for those
that everybody loves and knows.
If a poet splices in a poem,
it's also allowed,
though nobody knows 'em.
Otherwise think once, think twice,
before you commit the dreaded splice!