My original intention was to create a page on assonance, consonance, and alliteration, and I still intend to, but there are considerations about sound effects in poetry that come before those specialized ways of organizing sounds.  In all languages, spoken or written, the sond of the individual words, and the rhythm of the words used together have an effect upon how the reader or hearer responds.  In poetry, however, sound provides a major part of the meaning.    
    How do sounds mean?  That is too complex a matter to be explained fully here, but part of what we mean may be shown by comparing poetry to popular songs.  Sometimes a comedian will take the lyrics of a popular song and simply read them aloud like prose.  The result is absurd, something close to gibberish.  What is the point?  That popular songs are silly and absurd?  Probably, but  the point is not valid.  Without the music it is not the same statement, because the meaning was in the interaction between music and words.  Opera is meaningful to many who do not know Italian or German.  Music, of course, may be considered meaningful even with no words at all.
    Like music, poetry is a pattern of sound.  In poetry, however, the sound comes from the arrangement of the words themselves, and the effect is not from the sound of the words alone, but from the interaction between the sound and the meaning.  Poetry cannot be read by eye alone; it must be heard.  We must say the words, if only silently to ourselves.  To illustrate how close poetry is to the spoken word, try this experiment:  start writing a poem; then get a box of crackers and start eating them as you write.  Suddenly the writing will become very difficult, if not impossible.
    How is the sound of poetry produced?--partly by the sounds of the words and by the meter, partly by the natural rhythm of language with its longer and shorter pauses.  The most important pause, and usually the longest, is the break at the end of the line.  For poetry, though it may have the typical units of prose--phrases, clauses, sentences, paragraphs, even chapters--also has one unit that prose does not--the line.  One of the simplest definitions of poetry is "a kind of writing in which the lines do not come out to the end of the page."  This is probably a better definition than some, but it falls short in telling too little of what poetry does, and in placing too much emphasis on the written, as opposed to the spoken language.
    In free verse, the length and structure of a line of poetry is determined by the effect the poet wants to make; in traditional verse, it is determined by the meter.  There are a variety of reasons for ending a line at one place rather than at another, but in good poetry line length is never an arbitrary matter.
    So far we have been discussing the interaction of the sound of the word pattern with the meaning of the words at a level too deep to be consciously expressed.  At this level the comparison with music is an obvious one.  But the sound of poetry is also important at another level--a level closer to consciousness.  "The sound must seem an echo of the sense," Alexander Pope says in his Essay on Criticism.  In the eight lines below Pope gives examples of what he means:    
Soft is the strain when Zepher gently blows,
And the smooth stream in smoother numbers flows;
But when loud surges lash the sounding shore,
The hoarse, rough verse should like the torrent roar.
When Ajax strives some rock's vast weight to throw,
The line too labors, and the words move slow;
Not so when swift Camilla scours the plain,
Flies o'er the unbending corn, and skims along the main.
This kind of rhythmic appropriateness, though it is obvious when pointed out, usually has its effect without being consciously noticed.  If it is too obvious, it calls attention to itself as technique, and away from the poem as a whole.  The lines above were written to make a point; Pope is usually more subtle in his effects.  By the way, notice that the last line is an alexandrine, a twelve syllable line instead of ten like the rest.  The point he is suggesting is that the longer line actually moves more quickly than some of the shorter ones.  In the same poem he uses another alexandrine to make a very different point:

                       A needless Alexandrine ends the song,
                       That like a wounded snake, drags its slow length along.
    An example of overdone sound effects is Shakespeare's epitaph, in which the use of hollow, ghostly "o" and "oo" sounds help create an effect more comic than the anonymous poet probably intended:

                       Good friend for Jesus sake forbear
                       To dig the dust enclosed here:
                       Blest be the man that spares these stones,
                       And curst be he that moves my bones.

The "e" should be pronounced in the "ed" at the end of "enclosed."  This absurd poem was probably not even written specifically for Shakespeare, since it could apply to a baker as well as a poet, a woman as well as a man.  Probably it was something like, "$50.00 for the stone slab, and for an extra $5.00 I throw in a poem."  And then, "Oh, Daddy was a poet; he'd probably like that."
    The extreme form of making sound echo sense is the attempt to make the line of poetry actually imitate a sound.  This kind of imitation is called onomatopoeia.  An analogy in music to this kind of imitation is the tune, "Orange Blossom Special," in which the sound of a train's whistle, its bell, the clatter of wheels on a track are all imitated musically.  Probably the most famous example in poetry is this from Tennyson:

                       The moan of doves in immemorial elms,
                       And murmuring of innumerable bees.
These effects may be striking once in a while in a poem, but no poem can (or at least should) be made up entirely of them.  The doctrine that sound should echo sense should probably be followed largely in the negative--be sure that your sound does not work against your sense.  It is also a reminder of the most essential point to remember about writing poetry--sound, and how you use it, matters.
    The Essay on Criticism also offers examples f how the sound can detract from the line:

                       Though oft the ear the open vowels tire.

In this line the "e" should be pronounced in "vowels."  English was increasingly eliding such sounds, and the 18th century poet, when he wanted the reader to do so would indicate the fact by replacing the letter with an apostrophe.  This is a slow, dull, monotonous line.  Pope produces this effect by beginning most of the words with vowel sounds that are not cut off sharply, but rather fade away.  If an open vowel ends one word and then another open vowel begins the next word, as in "Though oft," the line moves even slower; first the reader must wait for one sound to die out, then pause, then begin another.  Pope cheats a bit with this, using other elements to slow the line as well.  Most of the consonants, "th," "r," "v," are also continuous sounds and contribute to the slow, gasping effect of the line.  It always surprises me how many such lines I find in poems submitted to Ship of Fools, but poetry workshops seem not to know how to deal with such issues, or even that there is an issue.  The best sound for a line is, of course, the one the context calls for, but this is an effect that a poet should very seldom want.
                       And ten low words oft creep in one dull line.

In this line Pope is showing that a long line made up entirely of monosyllables tends to have a slow, choppy, labored effect--by long line, I mean lines of ten or more syllables;
in shorter lines it is not really an issue.  Notice that Pope is cheating here too--he is using the long vowel sounds with consonant sounds that are also continuous, like "n" and "l."  As with most such observations, exceptions could be quoted, but it is a general fact that one two-syllable word can usually be pronounced more quickly and easily than two one-syllable words.
    Other generalities of more or less value could be made about sound in poetry, but these are probably enough to show that a line of poetry, even considered in terms of sound alone, is a very complex organism in which every word, every syllable, every individual sound plays a part.

    The button below leads to "Assonance, Consonance, and Alliteration, a further devolopment of much that has been discussed on this page.  ---Jack Hart