Why are limericks funny?

Limericks are a common poetic form, so common that many poets won't acknowledge them as poetry at all. Snobs.

The form of a limerick is a rhyming triplet divided by a rhyming couplet in the form a a b b a. The first second and third lines are three metrical feet and lines three and four are two metrical feet. A foot being three syllables, so 9, 9, 6, 6, and 9 syllables of which lines 1, 2 and 5 rhyme and lines 2 and 3 rhyme.

Confused? Me too. Here's even more than you need to know about the construction of limericks.

Time for an example.

A certain young man, it was noted,
Went about in the heat thickly-coated;
He said, 'You may scoff,
But I shan't take it off;
Underneath I am horribly bloated.'

- Edward Gorey, The Listing Attic in Amphigorey

As with so many things, I can find no definitive origin for limericks. Nor can I find any real reason why they're almost always funny. Or trying to be funny.

Some sources suggest that they are indeed named for Limerick, Ireland, after what sounds like a cheap advertising slogan, "Come all the way up to Limerick?" Or by soldiers returning to same from France in the 1700s.

The bawdy nature of many limericks is blamed on sailors and bar patrons and people who like to rhyme "Nantucket".

The popularity of limericks as a classsroom exercise was begun by Edward Lear with the publication of A Book of Nonsense (1845). The form of his poems does not follow that of modern limericks with the final rhyme being one from the first two lines, often the place name.

There was an Old Person of Ewell,
Who chiefly subsisted on gruel;
But to make it more nice
He inserted some mice,
Which refreshed that Old Person of Ewell.

Limerick (poetry) at Wikipedia

Edward Lear Home Page