Substitution (poetry)
Introduction In English poetry '''substitution''', also known as '''inversion''', is the use of an alien metric foot in a line of otherwise regular metrical pattern. For instance in an iambic line of "da DUM", a trochaic substitution would introduce a foot of "DUM da".
Trochaic substitution In a line of verse that normally employs iambic meter, trochaic substitution describes the replacement of an iamb by a trochee. The following line from John Keats's ''To Autumn'' is straightforward  iambic pentameter::To swell the gourd, and plump the hazel shellsUsing '°' for a weak syllable, '/' for a strong syllable, and '|' for divisions between feet it can be represented as:   ° / ° / ° / ° / ° /  To swell the gourd, and  plump the ha- zel  shellsThe opening of a sonnet by John Donne demonstrates trochaic substitution of the first foot ("Batter"):   /  ° °  / °  / °  / °  /   Bat- ter my  heart three- per- soned  God, for  youDonne uses an inversion (DUM da instead of da DUM) in the first foot of the first line to stress the key verb, "batter", and then sets up a clear iambic pattern with the rest of the lineShakespeare's Hamlet includes a well-known example::To '''be''', or '''not''' to '''be''': '''that''' is the '''ques'''tion::'''Whe'''ther 'tis '''nob'''ler '''in''' the '''mind''' to '''suff'''er:The '''slings''' and '''arr'''ows '''of''' out'''rage'''ous '''for'''tune'''In the first line the word ''that'' is stressed rather than ''is'', which would be an unnatural accent. The first syllable of ''Whether'' is also stressed, making a trochaic beginning to the line.John Milton used this technique extensively, prompting the critic F. R. Leavis to insultingly call this technique the Miltonic Thump.
Iambic substitution Sometimes the opposite substitution, of an iamb in place of a trochee, is found, as in the following lines from Shelley's ''Ode to the West Wind''::'''Thou''', from whose '''un'''seen '''pre'''sence the '''leaves''' '''dead''':Are '''dri'''ven, like '''ghosts from''' an en'''chan'''ter '''flee'''ing.Here the words ''the leaves'' are an iamb (da DUM) in a place in the line where normally there would be a trochee (DUM da).
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