I promised, a long time ago, a post on musical versus poetic rhythm, and I've lately been reading a fair amount of, shall I say, marginal scansion. So here's the short version: beat and stress aren't the same thing, and neither means in poetry what it means in music. I'll start the long version tonight. I won't ever finish it—though I think what I manage may be useful to some at least.
It's easy to show that a musical rhythm has very little necessary relation to any particular lyric sung to it. Consider that "Making Whoopee" and "Star of the County Down" were written (in the second case, first written down) in 3/4 time, and try to find a recording of either that isn't 4/4. Consider that it's relatively easy to sing the Declaration of Independence or the Gettysburg Address—in fact, almost any text—to the tune of "Greensleeves." Count how many beats per syllable there are in "Ooh, baby I love your ways" or "It wasn't God who made honky-tonk angels" or "We'll never give up, it's no use / If we're fucked up, you're to blame." One can always stretch a syllable over several beats, or divide a single beat among several syllables, and never deviate from, say, 6/8 time. But the downbeat and secondary stresses are nearly always in the same place in successive measures, and the time taken for every beat is the same unless either there are explicit instructions to slow down here or speed up there, or some particular musician or group of musicians decides there's some expressive reason to do so. If a group, they'd better all damn well do it the same way. I recently heard the Sam Bush Band do a tune in 7/4 time, and Sam warned the dancers to be extra careful.
But no one ever complained that some poet couldn't keep time.
People do complain that they hear 4 beats or 6 or some number other than 5 beats in a pentameter line, meaning that there are that number of strongly stressed syllables. They're usually right about the stressed syllables they hear, but that's only marginally related to the number of metrical stresses in the line. I've posted about this before, but links to individual posts in pre-2006 archives don't work, so I'll end tonight by quoting an earlier post which I'll use in the next few days to illustrate what I mean:
a brief IP demo. From sheer perversity on my part, all of the following examples are the first two lines of poems in Rebel Angels.
Yellow freesia arc like twining arms;
I'm buying shower curtains, smoke alarms,
Elizabeth Alexander, "Letter: Blues"
Who says a woman's work isn't high art?
She'd challenge as she scrubbed the bathroom tiles.
Julia Alvarez, "Woman's Work"
This is a sight that Wordsworth never knew,
whether looking down from mountain, bridge, or hill:
Bruce Bawer, "The View from an Airplane at Night, over California"
A motorcycle roaring in the distance—
I sigh myself. I loved her. More than Christmas,
Rafael Campo, "Aunt Toni's Heart"
She spent her money with such perfect style
The clerk's would gasp at each new thing she'd choose.
Tom Disch, "The Rapist's Villanelle"
"Get up!" "Marlene?" I smell the April rain
And squint half-dreaming at the windowpane
Frederick Feirstein, "Mark Stern Wakes Up"
"This must have been her bedroom, Mr. Choi.
It's hard to tell. The only other time
Dana Gioia, "Counting the Children"
No ornaments but the double bed and open
solitude found in older motels off-season
Emily Grosholz, "The Outer Banks"
Slow for the sake of flowers as they turn
Toward sunlight, graceful as a line of sail
R. S. Gwynn, "Release"
I bet you don't wear shoulder pads in bed.
I bet when we get over, we'll be bad!
Marilyn Hacker, "Wagers"
When my eyes rove in search of recognition,
what fills them, as if they were ears, not eyes,
Rachel Hadas, "Sentimental Education"
Some people as they die grow fierce, afraid.
The see a bright light, offer frantic prayers,
Andrew Hudgins, "The Hereafter"
That's enough: 12 pairs of opening lines from the first 12 poets in single anthology of contemporary formal verse. Considering substitutions, placement or lack of caesura, enjambment, and varying levels of stress, no pair consists of metrically identical lines, and no pair is identical to any other. Very few stray far from ordinary speech. Each pair quickly establishes a different mode and feel.
And every one is instantly recognizable as iambic pentameter.
An endless stream of ones carries no information, and neither does an endless random stream of numbers. What matters are variations within a recognizable pattern, and for poetry in English meant to read as if spoken by a human voice, no other line is as capacious as the pentameter.
Do I need to say that the above doesn't mean all poems should be IP? I didn't think so.