The real question should be: Why did Lear write limericks on 4 lines?
Let's
take a look at some of the limericks as Lear actually wrote them.
Bosh and Nonsense London: Allen Lane, 1982 provides holographic
examples.
A limerick
on two lines.
A limerick
on three lines.
A limerick
on four lines.
A limerick
on five lines.
A limerick
on, heaven forbid, six lines.
The answer
is, I think, that Lear wrote limericks on 2, 3, 4, 5, or 6 lines as his
mood and space on the page dictated.
Arthur
arthur@limericks.org
http://www.limericks.org/pentatette/reply.html