There are two types of pentameter used in poetry: iambic and dactylic. Iambic is the form most widely used in English and relies upon stressed and unstressed syllables. Dactylic is the form most used in ancient Greek and Latin; it relies upon syllable length. Such poetic forms are called pentameter because they have five feet per line.
A foot is the smallest unit of meter in poetry. There are many types of foot based on the number of syllables contained within. The smallest foot has only two syllables while the largest has four. Feet are further divided by how the syllables are expressed, whether they are stressed or based on length. Dactyls and iambs are two of many types of poetic foot.
An iambic foot consists of two syllables. The first syllable is typically unstressed, while the second is stressed. This is often represented as da-DUM with ‘da’ meaning unstressed and ‘DUM’ meaning stressed. This syllabic couplet is repeated five times to create a line of pentameter verse. The da-DUM foot can be two whole words, parts of one word or the end of one word and the beginning of another.
On occasion, the da-DUM rhythm can be reversed to create DUM-da. When this occurs, the next iambic foot tends to revert to the original rhythm. William Shakespeare used iambic pentameter a lot in his poems and plays.
There are a number of examples of him reversing the da-DUM rhythm including in “Richard III.” In a speech in the play, one line reads: “Now is the winter of our discontent.” This line has a DUM-da, da-Dum, da-da, DUM-DUM, da-DUM rhythm to it. Hamlet’s well-known speech, however, is more conventional with the one change: “To be or not to be, that is the question.” In this variation, there is a single da-DUM reversal with “that is.”
Dactylic pentameter is comprised of two half lines. Each half line consists of 2.5 feet. This means there are a total of six feet, but they comprise five whole feet, so it is still called dactylic pentameter rather than its closely-related cousin, the dactylic hexameter. The 0.5 foot of each half comes from a longum or heavy syllable added at the end of two dactyls.
A dactyl is composed of a long syllable followed by two short syllables. In the first half of a line of dactylic meter, either or both dactyls can be replaced with a spondee. A spondee is a pair of long syllables only. The final two feet comprising the second half-line must be composed of two dactyls and one longum.
Homer’s “Iliad” and “Odyssey” are classical examples of dactylic pentameter. There are few examples of dactylic verse in English for language reasons. Examples include Charles Kingsley’s “Andromeda” and Henry Wadsworth Longfellow’s “Evangeline.”