Poetic meter is not rocket science or brain surgery; it's not even completing your income tax form by yourself.  For many people, however, even many who have been writing poetry for a long time, it is looked upon as a mysterious and esoteric subject.  The following page will try to explain what it is and how it works in traditional western European and Amercian poetry, and how it has worked in some other traditions as well.
    First, meter is the rhythm of language arranged in an ordered manner.  For the ancient Greeks and Romans it was a matter of arranging the long and short syllables.  For Medieval Europe and since, it is the arrangement of stressed and unstressed syllables.  The stressed syllable in a word is the syllable that is emphazised.  You say de-PART, not DEE-part, or de-CAY, not DEE-cay.  These are both verbs.  English tends not to stress the first syllable of a verb, but usually does the first syllable of a noun.  If a noun is borrowed from another language, like de-COR, people tend to pronounce it DAY-cor.  (For some reason that pronunciation grates on my ear like it does for many people when Homer Simpson or George Bush say "nuculer.")  Pronounce other two-syllable words; see where the stress falls, then try pronouncing them with the stress on the other syllable.
    Now, consider a three syllable word--enmity.  We can stress it EN-mi-ty, or to use symbols, /xx.  But the third syllable is stronger than the second one; are you sure it's not / x /?  The fact is, stress is not entirely inherent in the word, at least not in all words.  "Sleepy" can only be pronounced with the first syllable stressed, but in many cases it depends on the other words and syllables around it.  In "enmity" the third syllable is a half stress, and could be scanned as / x \, the backward slant indicating a partial stress..  Poetry does not deal in half stresses.  In a word group like "enmity sucks," the pattern would be this: / x x /.  In a word group like, "enmity arouses" it would be / x / x / x.  The "ty" is so much stronger than the syllable before or after it that it comes off as a stress.  This is nothing mysterious--say the phrases aloud and listen to yourself.  We are not talking about anything mysterious, but rather about how you really speak in real life.
    Everything I've said about three syllable words of course applies to four and five syllable words, though these are less common in English in general, and especially in poetry which tends to a more concrete vocabulary, and therefore fewer really long, Latinate words.  The only difference is that the longer words nearly always have a secondary half-stress, while many three syllable words don't.  But what about one syllable words?  Most of these are unimportant words like "the" or "and" or "in" and so preferrably are unstressed, though they can be used as a stress if the words on either side of them are even weaker.  Ideally, though, stress falls on words that matter, and most one syllable words don't.  Pronouns are an exception.  Again, say a sentence, any sentence, and listen to where you put the emphasis.  Try revising the sentence a little and see if you can't make it more or less emphatic by substituting or rearranging the words.  I could say, change the words without changing the meaning, but in poetry the sound is part of the meaning, just as it is in song lyrics.
    Ok, let's start putting things together.  This isn't poetry, but it does have a clear meter--"Let's don't, but say we did."  The meter would be called iambic trimeter, and can be represented like this:  x / x / x /.  Now, we'll move on to actual lines of verse:

                                         In Flanders fields the poppies blow,
                                         Between the crosses, row on row.

Notice that this is the same stress pattern as in the example above, except that there are two more syllables in each line.  It would be called iambic tetrameter.  So, is everything iambic something?  No, there are other patterns, but in English the great bulk of poetry not free verse is iambic.    Here's an example of something else:

                                                           Dressed in yellow
                                                           Kissed a fellow.

This is the reverse of the lines we have been looking at-- / x, instead of x /.  But this is jump rope rhyme, which is always in trochaic meter, in this case, trochaic dimeter.  Early in the 20th century Vachel Lindsay made a great reputation as  modern poet by using such rhythms in poems like "The Congo," but both he and the poem have largely faded from our sense of what modernism was about.
    There are four metrical patterns recognized in traditional English poetry.  Here is the stress pattern for each:

                                               iambic:        x /
                                               trochaic:     / x
                                               anapestic:  x x /
                                               dactylic:    / x x

In addition to the four kinds of metrical feet, there is also the spondee-- / /, two stressed accents falling together as a unit.  There are not a lot of English two syllable words in which the stress is nearly equal--bulldog, hemlock, and a few others.  More often a spondee comes from two stressed words falling together.  Since the spondee does not itself have a rhythm, its presence does not change the meter of the line.
    As you can see these metrical feet only involve two or three syllables, much shorther than most poetic lines.  This is where the other set of terms come in:


These simply mean one, two, three, four, five, and six.  The number could go on up, but few English lines of poetry are longer than hexameter, and the ones that are are mostly free verse.  In other words, these term tell you how many metrical feet are in a line.  The line, "Why do we grieve that friends must die" is eight syllables, made up of four iambs.  Therefore, it is iambic tetrameter.  "The hungry judges soon the sentence sign," is ten syllables, five of them stressed, and is iambic pentameter--so common a line length that most people have heard of it.
    But what about these lines from Byron's "Destruction of Sennacherib"?

                                    The Assyrian came down like the wolf on the fold,
                                    And his cohorts were gleaming in purple and gold.

This is a much less familiar meter, but not hard to figure out--how many stresses in what pattern?  Four stresses in an anapestic pattern, or anapestic tetrameter.  There are not a lot of serious poems in anapestic--it is too bouncy.  "Not a creature was stirring, not even a mouse," sticks in the mind, but it is not really grand poetry.  Anapestic seems to cry out for parody, and Robert Southey's "The Old Man's Blessings and how he Gained Them" is far less known that Lewis Carroll's parody of it, "You are Old Father William."  Here is a whole poem in anapestic meter, Isaac Watts' "The Sluggard:"

                                'Tis the voice of the sluggard, I heard him complain,
                                You have waked me too soon, I must slumber again.
                                As a door on its hinges, so he on his bed,
                                Turns his side and his shoulders and his heavy head.

                                 I passed by his door and saw the wild brier,
                                 The thorn and the thistle grow broader and higher.
                                 The clothes on his back are turning to rags,
                                 But still he sleeps on `til he starves or he begs.

                                 I paid him a visit, still hoping to find
                                 He had made some attempt at improving his mind.
                                 He told me his dreams, spoke of eating and drinking,
                                 But scarce reads his Bible, and never loves thinking.

    This is pretty bad, and really does deserve Lewis Carroll's,

                                 'Tis the voice of the lobster; I heard him declare,
                                  You have baked me too brown; I must sugar my hair.

One interesting feature of Watts' poem is the strong break in each line, for which there is a technical term, caesura.  There are two strong stresses before each break, and two after, like in Beowulf, and other Anglo-Saxon poems.  The Anglo-Saxons, however, sound more dignified, since they do not write in anapestic meter.
    The most significant poetic form to use anapestic is the limrick.  Most of us know it best from the poetry on bathroom walls, but I would be embarrassed to use any of those examples, however well known.  Here is the one President Kennedy quoted in his inaugural address:

                                                There was a young lady from Niger
                                                 Who smiled as she rode on a tiger.
                                                 They've returned from the ride
                                                 With the lady inside,
                                                 And the smile on the face of the tiger.

This is an example of a whole poetic form, and a very rigid one at that.  The first metrical foot is always an iamb, and the rest of the poem is all anapests, lines one,
two, and five are anapestic trimeter, lines three and four, anapestic dimeter.  Notice that the first unit is counted, even though it is not properly an anapest.  A weak stress at the end is also not counted.  (An iambic pentameter line with an extra unstressed syllable at the end, by the way, is called a hendecasyllable.  It was probably not a coincidence that Robert Frost wrote a poem about his show hens in hendecasyllables.)  Here is another limerick without the extra syllable:

                                                 An epicure dining at Crewe
                                                 Found quite a large mouse in his stew.
                                                 Said the waiter, "Don't shout,
                                                 And wave it about,
                                                 Or the rest will be wanting one too."                                                
    Unlike with most poetic forms, here the meter has to be followed exactly.  The place name at the end of the first line, by the way, is not essential--it is merely a convenient way of establishing the rhyme.  The limerick was popularized by Edward Lear's Book of Nonsense, and is considered unsuited in its bouncy, jingling tone for any serious use, though it's first known appearance was an uplifting work dealing with a number of philanthropic ladies called, "Twelve Worthy Old Women of London," or something very close to that.  But I intend to devote a separate page to poetic forms, and so will get back to meters.
    I have already touched upon trochaic meter.  Compared to the rather flat and "normal" sound of iambic, trochaic seems primitive and incantatory with its insistent and drum-beat like rhythm.  The one really famous example of it is Longfellow's Hiawatha, a book-length poem that was very popular throughout the English-speaking world in the ninteteenth and early twentieth centuries.  It might still be, except that those who produce literature textbooks avoid it as nearly as possible.
    Longfellow was very proficient with languages and read the German translation of the Finnish epic, the Kalevala.  This work made up from very ancient sources creates a picture of a primitive, forested, mythic world that sounds rather like that of American woodland Indians, and the meter of the poem with its very basic four beat line in trochaic meter seemed the perfect verse form to express that material.  Longfellow, himself, was planning a book-length poem based on Indian myth and legend, and the trochaic tetrameter of the Kalevala seemed like the perfect verse form for it.  Here are some lines from Hiawatha:
Through the tranquil air of morning,
First a single line of darkness,
Then a denser, bluer vapor,
Then a snow-white cloud unfolding,
Like the tree-tops of the forest,
Ever rising, rising, rising,
Till it touched the top of heaven,
Till it broke against the heaven
And rolled outward all around it.
    Although this sounds nothing like real Indian poetry, it became the standard way of representing it.  I even remember a Donald Duck comic from my childhood in which Donald and his uncle, Scrooge discovered a tribe of pigmy Indians that spoke exclusively in trochaic tetrameter, and in phrasing that echoed Longfellow's poem.
     Dactylic as a meter hardly exists in English aside from one form, dactylic hexameter.  English does not normally accomodate such a long line, and no English poet would have ever thought of it without the example of the ancient Greek and Roman poets.  The form has a high prestige from its use in the Iliad, the Odyssey,
the Aeneid, Ovid's Metmorphosis, and lesser ancient works.  Experiments with it never seemed to go well, however, and translations of the ancient poems usually ended up being translated into iambic pentameter, often as rhymed couplets--an awkward fit, since one iambic pentameter line is short to represent one of the original lines, and a couplet is too long.  The best known examples of the form in English are by Longfellow in such poems as Evangenline and The Courtship of Miles Standish.  The line usually quoted in textbooks on meter is this one from Evangeline:

               This is the forest primeval, the murmurring pines and the hemlocks.

The metrical pattern is,  / x x    / x x    / x x    / x x    / x  x    / / .  Notice that though this is called dactylic hexameter, there are only five dactyls.  The last metrical foot is a spondee.  Longfellow has managed five dactyls in a row--why does he break down on the last one?   
    The fact is, he hasn't.  A long series of long lines, all of them falling off at the end with two weak syllables would be a very miserable sort  of verse.  In finishing with a spondee, he is merely following the example of his ancient predecessors.
    One reason that this form has never worked really well in English may be that in so long a line, it is very easy to begin reading the stress as the end of a unit instead of as the beginning, and then the rhythm becomes anapestic, like "The Night Before Christmas."  It is especially easy to read it that way, since anapestic is a lot more emphatic than dactylic.  This was not a problem for the ancients, since they handled the line a little differently.  The rule for them was that the last foot was always a spondee, and the next to last always a dactyl.  The other four could be either--more spondees made the line quicker and harder, more dactyls made it slower and more flowing.  Thus for the ancients the line could have as few as thirteen syllables, or as many as seventeen.  But however great the portion of spondees, it is still dactylic, because only the dactyls have any rhythm.  Here is the opening of the Aeneid, with the long syllables indicated by __.

                         Arma virumque cano, Trojae qui primus ab oris

The meter is:  __ __    __ x x    __ __    __ x x    __ x x     __ __, three dactyls and three spondees. 
    I wondered why the meter could not be written in English in a way more like the ancients did it than the way Longfellow did, and so tried it.  I produced two poems, probably about 30-40 lines altogether, enough to see that it could be done.  They were not really first-rate, however, and without writing enough to make the form familiar and natural, I still did not know whether really good poetry could be written in that way.  What discouraged me from more effort was the fact that centuries of English poets had been trained on Greek and Latin models; if the form really was capable of great things, why hadn't someone noticed long before?
    An approach to meter that is clearly workable in English, however, is the old Germanic alliterative verse.  For one thing, it is native to English, and is used effectively in Beowulf, The Wanderer, and other Old English poems.  The language was rather different then, but alliterative verse had a revival in the fourteenth century when the language was much closer to modern English.  The most common line of old alliterative verse is a four stress line with a strong break in the middle, leaving two stresses before the break and two after.  The unstressed syllables are not counted, though in general fewer are better than more.  A great deal has been made of Gerard Manley Hopkins' "innovation" of only counting the stressed syllables, what he calls sprung rhythm, but in fact it is always the stresses that are of primary importance.
I am not quite sure of what all rules were involved in Old English alliterative poetry, other than that at least one initial stressed consonant sound had to be repeated in the second half-line.  In the alliterative revival, the rule was tighter.  Both stresses in the first half line alliterated, and one or both in the second half-line.  Unless handled with considerable skill, the language tends to rattle along, falling much of the time into anapestic rhythms.
    I can speak with more precision about Old Norse poetry.  Like other old Germanic poetry, the most important line was the four stress line with the medial break, though they managed to produce a surprisingly large number of verse patterns, most of them involving the four stress line in one way or another.  In fornyrdislag meter the poet writes in stannza of four lines, each line consisting of two half-lines.  One or both stresses in the first half-line alliterates with the first stress in the second half-line, but not with the second stress.  For s alliterations, if the s is followed by an explosive consonant--b, t, k, p, then the s it alliterates with must be followed by the same consonant.  The two th sounds cannot be alliterated with each other.  Sh is not treated as an s sound at all, and must alliterate with another sh.    Now and then, initial vowels are allowed to serve for the alliteration, but instead of repeating the same vowel a different one should be used.  Alliterating the first stress of the second half-line and avoiding alliteration on the second draws attention to the middle of the line.  When one neglects this rule, as Henry Adams Bellows does in his translation of the Poetic Edda, the result is to move the emphasis to the end of the line like in standard metrical verse, and to allow anapestic rythms to take over to the detriment of the dignity and subtltry of the language.
    A second meter that was very widely used was ljodahattr.  It may sound similar in description but is quite different in impact, being a much quicker, more quotable form.  For that reason it was favored for charms, spells, maxims and such, as well as for narrative.  This too is a four line stanza, lines one and three working like they would in fornyrdislag meter.  Lines two and four consist usually of three stresses.  Any two two or three of the stresses are alliterated.  This form is far easier two write and has a much more emphatic rhythm.  It sounds a great deal like English ballad meter, which also consistes of four line stanzas alternating between four stress lines and three stress lines.  In ballad meter, of course, lines two and four rhyme, but the alliteration produces much of the same feel.  At times both of these meters appear in the same poem used for different kinds of contexts.  This is from my translation of the latter part of the "Lay of Fafnir" and incorporates both forms--listen to the difference in sound: 
The first nuthatch speaks:
"Wise were he    if heed he took
To sound advice    we sisters give:
Do right by self,    make ravens glad.
See the ears,    suspect the wolf."

The second nuthatch speaks:
"Less wise to me    the warrior seems,
Than battle-leader    ought to be,
If brother share not    brother's fate,
When he has been    the bane of one.

The third nuthatch speaks:
"A fool is he    if he should spare
The foemen of the folk.
There Regin lies,    and wrong intends,
And he, unguarded from guile.
    Yes, I know, nuthatches are usually not this informative, but Sigurd has just drunk the dragon's blood, and now can understand the language of the birds.
    There is doubtlessly a lot more that I could say, and even more that others could say about metrics, but perhaps this is enough to give the general idea.  Of course metrics by themselves are only part of the story.  They have to be discussed in connection with verse forms, and this essay has done that here and there.  My intent, however, is to devote a second page to stanza forms, which I hope will be forthcoming very soon, though one never knows.  ---Jack Hart