English language poetry uses five basic types of meter. Meter is the pattern of accented and unaccented syllables in a work. Words naturally have stressed and unstressed syllables, and poetry puts these stresses together to give a poem rhythm. Unforced poetry places the stresses where they fall in ordinary speech, so that a poem sounds like something someone might actually say.
The purpose of a particular meter may be to accentuate the rhythms of someone's speech, to emphasize the meaning of certain words, or to reproduce the rhythm of wind blowing, men marching or waves breaking on a rocky shore.
The five main types of meter are iambic, trochaic, spondaic, anapestic and dactylic. These terms describe combinations of two or three stressed and unstressed syllables that each form a foot. The feet are generally repeated (with careful variation) throughout a poem to produce its rhythm, increase its music and communicate its vision.
Iambic is the most common meter in English poetry. Shakespeare uses almost nothing else, at least when he gives a noble character a good speech. In an iambic foot, an unstressed syllable will be followed by a stressed one: "If music be the food of love, play on."
Readers must take the number of feet in a line into account when they describe the meter of a poem. An iambic line with two feet is iambic dimeter, three is trimeter, four is tetrameter, five is pentameter, six is hexameter, seven is heptameter and eight is octameter.
However, poems are not necessarily written in one solid block of meter-in fact great poets seldom write that way. A poet may illustrate sudden exclamations or startling turns of thought with spondees, which are metric feet containing one accented syllable and nothing else. "Break, Break, Break, on the cold gray stones, oh sea." In this famous line, Tennyson is reproducing the rhythm of the waves on a rocky shore, and also illustrating the way the death of a friend has abruptly cut the poet off from life and warmth.
Trochaic stresses the first syllable in a two syllable foot. For instance, in the line "By the shores of Gitchee Gumee," Longfellow uses a sing-song rhythm to emphasize that he is telling a story, not writing a biography of Hiawatha (though of course Hiawatha was a real person). The rhythm evokes a traditional storyteller.
Limericks and many Dr. Seuss stories use anapests. The foot follows two unstressed syllables with a stressed one: "The Assyrian came down like a wolf on the fold." Byron uses a galloping meter to convey the way the attack was joined, in The Destruction of Sennacherib.
Evangeline is written in dactylic feet, which consist of a stressed syllable followed by two unstressed ones. 'This is the forest primeval, the murmuring pines and the hemlocks.' Notice how Longfellow ends the line with a spondee, rather than letting it die quietly away.
Meter involves a reader in a poem. It leads him or her to follow the pattern, while it sets up an expectation of the way the words will come. However, the shifts and changes in meter often show the poet's mettle best, so they are where an attentive reader will stop and take notice.