Traditonally, the opening lines of a poem announce and establish its meter. In these opening lines, trochaic and (possibly) spondaic substitution threaten to unseat iambic pentameter altogether. We are drawn out of conflict in the nick of time by the perfectly iambic third line. The fourth line retains that regularity and trumps it: there the iambic finally becomes emphatic enough to take over the rhythmic rhetoric of the poem. 

Proponents of the spondee, such as Annie Finch, argue that scanning a spondee at the end of line 1, and another created by rhetorical stress on not in line 2 is the best way to show this rhythmnic and emotional conflict. If you scan with three levels of stress, you can make the rhythm visible in another way: by noting the mounting stress at the end of each of those first two lines. In the phrase of true minds each word receives more stress than the one before it. A similar effect is achieved in line two. 

Lines three and four, however, end quite differently: with the exception of a slight promoiton on it, no syllable contests its status, and the unstressed syllables toward the ends of those lines are notably weak and retiring. After a grand and disturbing entrance, the poem is getting down to business.

Finch makes a similar argument for inclusion of a phyrrhic foot in the same poem. Is it

IT is | the STAR | to EV | ry WAND | ering BARK    or

It is | the STAR | to EV | ry WAND | ering BARK    ?

Finch argues that "[t]he first foot is not a trochee; to scan it as such would obscure the earnest, hopeful, thwarted stretch of the second syllable towards a stress, and the consequent increase in energy that finally accompanies the awaited stress on 'star.'" (Baker 72) Others argue that what she is talking about is a rhythmic affect distinct from meter, though one of its effects. This line of thought would have it that we must first recognize the difference between meter and rhythm in order to feel the tension between them.

Of course, except when pressed for a scansion we are free to hear and adore such affects and effects with no necessity to make up our minds about their ontological status.

THE UNEQUAL FETTERS 

Cou'd we stop the time that's flying
  Or recall it when 'tis past
Put far off the day of Dying
  Or make Youth forever last
To Love wou'd then be worth our cost.

But since we must loose those Graces
  Which at first your hearts have wonne
And you seek for in new Faces
  When our Spring of Life is done
It wou'd but urdge our ruine on

Free as Nature's first intention
  Was to make us, I'll be found
Nor by subtle Man's invention
  Yield to be in Fetters bound
By one that walks a freer round.

Marriage does by slightly tye Men
 Whil'st close Pris'ners we remain
They the larger Slaves of Hymen
  Still are begging Love again
At the full length of all their chain.

Note the pattern in the first stanza: four "headless" tetrameter lines (two with feminine rhymes making them trochaic, two with masculine rhymes making them headless and unidentifiable as iambic or trochaic), followed by a perfect iambic tetrameter:

 COULD we STOP the TIME that's FLYing
   OR reCALL it WHEN 'tis PAST
 PUT far OFF the DAY of DYing
   OR make YOUTH forEVer LAST
 To LOVE wou'd THEN be WORTH our COST

Despite the presence of only one fully iambic line, we can describe this poem as iambic according to Hartman's rule of thumb. The first four lines give us no metrical assurance and the 5th line resolves that tension into iambic conclusion. What matters about this structure, however, is not what name we choose to give to it: what matters is that the metrical change in the last line simultaneously reinforces its quality of conclusion and subtly undercuts the illusions proposed in the more emphatic, falling, headless rhythm.

In the first line of the next stanza, readers in our day, unused to reading  metrical signals, might naturally start off: "But SINCE we MUST..." and run smack into "loose" (i.e. "lose") where the iambic falls apart. In fact, the meter of the first stanza provides perfect instruction on how to read this one: 

 BUT since WE must LOOSE those GRACes
   WHICH at FIRST your HEARTS have WON
 AND you SEEK for IN new FACes
   WHEN our SPRING of LIFE is DONE
 It WOULD but URDGE our RUine ON

The pattern continues neatly through the third stanza as she proclaims her unwillingness to submit to an unnatural inequality --the only variation being enjambment. In the last stanza, however, grammatical stress suddenly pops up and bucks against the meter:

 MARriage DOES but SLIGHTly TIE men

is the ideal pattern. But who could read it without adding stress to the last word, in contrast to "we" in the next line? To my ear at least, no pattern of stress in this line makes it comfortable in the smooth and consciously artificial metric that has been established over three stanzas.  (MARiage DOES but SLIGHTly tie MEN?  MARriage DOES but SLIGHTly TIE MEN?) Thus the genius of this line lies precisely in its uneasiness. True to the Augustan aesthetic, the poem has expressed its complaint in a light and witty manner. Here, resentment lodges rhythmically, metrically, like a small rock under a carpet. And the final line surprises again. The expected pattern would be:

 At THE full LENGTH of ALL their CHAIN

which almost no one would take seriously.  Breaking the pattern by reversing the first foot is possible:

 AT the full LENGTH of ALL their CHAIN

but when the whole stanza is read this is awkward and robs the line of even as much closural force as the last lines of previous stanzas. Further possibilities are that either a double iamb or a reversed foot and a spondee are intended. If not intended, certainly they stand in ghostly counterpoint, speech stress rising up against meter as the woman rises against the man. 

 At the FULL LENGTH of ALL their CHAIN.

 AT the FULL LENGTH of ALL their CHAIN

It is interesting to compare this poem to my earlier dyad, Campion and Donne. Its prosody is superficially much closer to Campion, and its genre, the woman's complaint, requires neither an individualized speaker nor a dramatic prosody. And yet, suddenly, in those last two lines, we stumble on the suggestion of both. 

Here's another by Finch:

This to the Crown, and blessing of my life,
The much lov'd husband, of a happy wife.
To him, whose constant passion found the art
To win a stubborn, and ungrateful heart;
And to the World, by tend'rest proof discovers
They err, who say that husbands can't be lovers.
With such return of passion, as is due,
Daphnis I love, Daphnis my thoughts persue,
Daphnis, my hopes, my joys, are bounded all in you:
Ev'n I, for Daphnis, and my promise sake,
What I in women censure, undertake.
But this from love, not vanity, proceeds;
You know who writes; and I who 'tis that reads.
Judge not my passion, by my want of skill,
Many love well, though they express itt ill;
and I your censure cou'd with pleasure bear,
Wou'd you but soon return, and speak itt here.

Note how she employs the conventions in this apparently sincere poem.  She portrays herself as "stubborn and ungrateful," requiring much wooing; she addresses "the World;" she calls her husband "Daphnis," a pastoral convention oft employed to at once idealize and disguise an illicit lover; she implies that for a woman to write love poems is objectionable, but her passion for him requires her to yield : apparently he has requested that she write him a poem--so writing becomes a stand-in for sexual yielding; she apologizes for her want of skill, even as she deploys her skill; and she welcomes his censure if it comes in a package with his presence. 

In this poem the conjunction of metrical and speech stress is quite firm, and, again, where they threaten to diverge she exploits the tension fruitfully.  In line 2, for example, two rhythms are overlaid: 

 The MUCH LOV'D HUSband, of a HAPpy WIFE  versus
 The MUCH lov'd HUSband, OF a HAPpy WIFE

And in line 8 the two reversed feet (initial and after the caesura) create another rhythmic unit in counterpoint to the meter: /uu/,/uu/

 DAPHnis i LOVE, DAPHnis my THOUGHTS perSUE

She does, however adhere to the period style: she avoids anapestic substitutions and spondees, and her primary device remains the caesura (whose placement varies from after the first foot to the middle of the fourth foot, sometimes weak, sometimes strong, as many as three in a line). Three lines have reversed first feet: the two lines beginning "Daphnis," which makes of the name a cry; and "Many love well," which provides a variation in pattern to set us up for the ending.

---

A useful exercise with Browning’s dramatic monologues is to type them out by phrase.  Thus

 Well, if the marks seem gone,
 ‘T is because stiffish cock-tail, taken in time,
 Is better for a bruise than arnica.**  **A herb
 There, sir! I bear no malice: ‘t is n’t in me.
 I know I acted wrongly: still, I’ve tried
 What I could say in my excuse,--to show
 The devil’s not all devil . . . I don’t pretend,
 He’s angel, much less such a gentleman
 As you, sir! And I’ve lost you, lost myself,
 Lost all-

is written as:

 Well,
 if the marks seem gone,
 ‘t is because stiffish cock-tail,
 taken in time,
 is better for a bruise than arnica.
 There, sir!
 I bear no malice:
 ‘t is n’t in me.
 I know I acted wrongly:
 still: I’ve tried 

This helps to show the virtuosity of Browning’s prosody, how he stretched meter toward speech without ever quite breaking it.  It also shows what an inferior poem the same words would make if reduced to phrase-determined “free verse.”

---

Metrical poets of our century also have a world of possibilities to choose from--and therefore their poems must be scanned with a good ear and an open mind.  Mostly regular poems may have irregular lines in them. Lines with many unstressed (or very lightly stressed) syllables may tend toward accentual meter. In some cases, these moves are intentional and highly affecting. In others, they reflect nothing more than a general desire to remain in the metrical tradition without imposing too much rigor on the poem. (And by late 20th century standards, it doesn’t take much metrical rigor to be considered too much by many readers.) The discussions below owe much to Gross & McDowell.

Here is the famous opening of T.S. Eliot’s “The Waste Land:

 April is the cruelest month, breeding
 Lilacs out of the dead land, mixing
 Memory with desire, stirring
 Dull roots with spring rain.

We might convince ourselves to hear five stresses in the first line, but the result isn't very satistactory as a perception of either spoken or metrical English:

    x AP | ril IS | the CRUEL | est MONTH | BREEDing 

Four stresses and four feet tell us more about what the line sounds like, showing both the run of three unstressed syllables early and the decisive final reversed foot:

    APril | is the CRUEL | est MONTH | BREEDing 

The second line is similarly ambiguous as to four vs. five stresses, and it’s hard either way to rationalize into feet. Maybe it's trochaic:

    LIlacs | OUT of  the | DEAD land | MIXing 

So let’s go to line three:

    MEMor | y AND | deSIRE | STIRring

Again, as in the first line, four feet, with 2 each of iambic and trochaic.  Things are definitely “mixing.” The speech stress on “and” is slight, but discernible and as a metrical stress it’s perfectly acceptable. Next:

    DULL ROOTS with SPRING RAIN

Whoops. Four beats, yeah, but no sign of accentual-syllabic meter, iambic or trochaic. No way you can make it four feet except by the weirdest of scansions--only one unstressed syllable to share among four stresses. So what is it? Well, what’s consistent? The number of stresses per line. Which makes it, in fact, an accentual meter. What makes the passage metrically interesting is that the ear dwells in the gray zone for three lines, not sure what it’s hearing, not sure what the pattern is, until the fourth line resolves the question. 

This aural ambiguity corresponds to emotional and spiritual ambivalence in the poem. We start with line one, wondering why or how April is cruel. The next lines begin to explain that, and the end of the explanation falls on the heavy, unarguable thud of the fourth line. To a reader attuned to the nuances of prosody and their history, the very return to the heavy thud of four strong stresses may have emotional implications. 

With the fourth line so heavy-handed, the old Anglo-Saxon meter seems a primitive thing, linked to the cruelty of mortality, the deception of spring when it figures hope. It alludes to an agricultural reality far removed from the effete consciousness that emerges as the poem progresses, and it links to the Anglo-Saxon Fisher-King myth that recurs throughout the poem. We don’t know that yet, if we’re reading the poem for the first time. But we do know how it feels.

William Butler Yeats in his early books was at times afflicted by a dreary, padded hexameter line, whose rhythms matched the vague romance of the Celtic Twilight  By the end of his career he had evolved to an opposite sound: accentual meters, short lines, and brilliantly counterpointed syntax. He began with lines like:

 And the flame of the blue star of twilight, hung low on the rim of the sky

Four prepositions, three articles, and a conjunction! a prize winner.  In his turning-point volume, Responsibilities, published in 1914, we still find hexameters, but they are more firm, more subtle, and their metrical moves more necessary.  These lines are from “The Magi”:

Sounds like a different poet. Notice that Yeats, like Milton and others before him, followed a principle of elision whereby certain syllables ordinarily spoken in performance do not count in scansion. (Hovering, Calvary, mystery, and bestial are all (metrically) two-syllable words. (In the 19th century many poets marked their elisions with apostrophes: hov’ring, e.g., which Yeats did not do.) Whether Yeats, an Irishman, actually pronounced them thus (hov’ring, Calv’ry, etc.) is a different quesion. The convention is a metrical one, not dependent on the accent of the poet. Thus we scan:

 And ALL | their HELMS |of SIL | ver HOV |ering SIDE | by SIDE,

 And ALL | their EYES | still FIXED | HOPing | to FIND | once MORE,

 BEing | by CAL | vary’s TURB | uLENCE | unSAT | isFIED,

 The UN | conTROLL | able MY | stery ON | the BEST | tial FLOOR.

Notice that in the first two lines speech stress and metrical stress coincide: we hear them all clearly. In line three, the last syllable of turbulence is so lightly stressed as to cause a little rock in the road. In line four we hear only four strong speech stresses:

 The unconTROLLable MYstery on the BESTtial FLOOR

The line scans just fine as hexameter, but its spoken rhythm is quite different--it is counterpointed. The rock in the road has turned into a boulder: this line is cut off from the classical world of hexameter, so not only what the line says but how it sounds pushes us forward into the 20th century. And besides the bestiality of 20th century horrors, we are reminded by those four strong speech stresses of a primitive past, figured by the shadow of the old English meter--a shadow that is made somewhat more substantial by the internal rhyme between two of the stressed words, uncontrollable and bestial, reminding us of the old meter’s alliterative pattern.

In “Easter 1916” Yeats used a three beat line in which iambs and anapests interchange freely.

I have met them at close of day
Coming with vivid faces
From counter or desk among gray
Eighteenth century houses.
I have passed with a nod of the head
Or polite meaningless words,
Or have lingered awhile and said
Polite meaningless words,
And thought before I had done
Of a mocking tale or a gibe
To please a companion
Around the fire at the club,
Being certain that they and I
But lived where motley is worn:
All changed, changed utterly:
A terrible beauty is born.

It can be scanned in feet, as an accentual-syllabic poem, or it can be scanned as accentual, marking only the stresses. Does it matter? In his late poems Yeats paid little attention to syllable count and moved firmly into an accentual meter: this poem can be seen as a step on that path. But probably more important than trying to categorize the poem’s meter is to recognize the delicacy of the ear at work here. Notice the unaccented syllables: “emphatic upbeats,” G&M call them, or “delicate end assonance.” Yeats is also known for superb syntactical control: no “flaccid long sentence or...monotonous short one.” The placement of the caesura, and the relationship of line and sentence vary infinitely and expressively, guiding the reading voice in pace, emphasis, melody:

We know their dream; enough
To know they dreamed and are dead;
And what if excess of love
Bewildered them till they died?

The lines each have three beats, but the phrases fall very differently. The first line begins with a 2-beat phrase, followed by a caesura. The last word is the start of a 4-beat phrase that completes itself on the next line. And the last two lines make a phrase together, with six beats--an echo, after all, of the old hexameter. Thus while the meter says 3/3/3/3, the syntax says 2/4/6, and the 4 says a very different thing than the 6.

One of the criticisms of accentual poetry is that it cannot manage much variety in the lines. The lack of control over unaccented syllables and secondary stresses necessitates a more heavy-footed line than can be presented in accentual-syllabic verse -- to lighten the beat is to risk loosing meter altogether. These masterful lines by Yeats demonstrate how syntax, counterpointed with line, can create efects of speed, lightness, and emotional variation in that put the lie to this complaint.

Much apparent free verse is actually written in loosely iambic lines of varying length.  Such as:

 Against the shimmering heat,
 each separate leaf
 is bright and cold,
 and through the bronze
 of shining bark and wood
 run the fine threads of gold.

These lines can easily be described as trimeter and dimeter, and the passage is further unified by sound: heat/leaf, bright/shining/fine, separate/bright, bright/bronze/bark, wood/gold, the o sounds of cold, bronze, wood, gold. In the following passage by the same poet (H.D.--Hilda Doolittle) notice how the prose-like phrasing tightens down to two-beat strong stress when the emotion climaxes:

     few were the words we said
 but the words are graven on stone,
 minted on gold, stamped upon lead;

     he, Achilles, piling brushwood,
 finding an old flint in his pouch,
 “I thought I had lost that”;

 few were the words we said,
 “I am shipwrecked, I am lost,”
 turning to view the stars,

 swaying as before the mast,
 “the season is different,
 we are far from--from--”

 let him forget
 Amen, All-father,
 let him forget