The Nonsense verse reference article from the English Wikipedia on 24-Apr-2004
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Nonsense verse

Nonsense verse is a form of poetry, normally composed for humorous effect, which is paradoxical, silly, witty, whimsical or just plain strange. However not all humorous verse is nonsense. For instance a poem like

Algy saw the bear.
The bear saw Algy.
The bear was bulgy.
The bulge was Algy.

is humorous but not nonsense. Whereas

The elephant is a bonnie bird.
It flits from bough to bough.
It makes its nest in a rhubarb tree
And whistles like a cow.

is classic nonsense being based on the incompatibilty of word pairs such as elephant/flit, rhubarb/tree, whistle/cow which make grammatical sense but semantic nonsense.

The poem ...

One fine day in the middle of the night,
Two dead men got up to fight.
Back-to-back they faced each other,
Drew their swords and shot each other.
A paralyzed donkey walking by,
Kicked a blind man in the eye,
Sent him through a rubber wall,
Into a dry ditch and drowned them all.

... makes even more extreme use of word incompatibility by pairing a number of polar opposites such as day/night, paralyzed/walking, dry/drowned, in conjunction with lesser incompatibilities.

Other nonsense verse may make use of nonsense words -- words without a clear meaning or any meaning at all. Lewis Carroll and Edward Lear both made good use of this type of nonsense in some of their verse.

The first verse of Carroll's Jabberwocky ...

`Twas brillig, and the slithy toves
Did gyre and gimble in the wabe:
All mimsy were the borogoves,
And the mome raths outgrabe.

... illustrates this nonsense technique perfectly, despite Humpty Dumpty's later explanation of some of the unclear words within it.

However not all nonsense verse relies on word play. Some conjures up nonsensical situations, for instance Edward Lear's fine poem, The Dong with the Luminous Nose has a perfectly comprehensible chorus.

Far and few, far and few,
Are the lands where the Jumblies live;
Their heads are green, and their hands are blue
And they went to sea in a sieve.

What is the significance of the colour of their heads and hands? Well, none really. It's just mellifluous nonsense.

Likewise Christopher Isherwood's poem ...

The common cormorant (or shag)
Lays eggs inside a paper bag.
You follow the idea, no doubt?
It is to keep the lightning out.
But what these unobservant birds
Have never noticed, is that herds
Of wandering bears may come with buns
And steal the bags to hold the crumbs.

... makes grammatical and semantic sense and yet lies so earnestly and absurdly that it qualifies as complete nonsense.

There is a long tradition of nonsense verse in English. Many nursery rhymes are nonsense. For instance ...

Hey diddle, diddle,
The cat and the fiddle.
The cow jumped over the moon.
The little dog laughed to see such fun,
And the dish ran away with the spoon.

Limericks are probably the best known of nonsense verse, although the form tends to be used for bawdy or straightforward humorous effect nowadays rather than for nonsensical effect.

Among the poets noted for nonsense verse are Edward Lear, Lewis Carroll, Ogden Nash and Spike Milligan.