An iamb can be best described as a unit of measurement or a type of rhythm used in poetic verse that consists of two syllables, the first unstressed and the second stressed. It is a type of poetic foot, which is usually a group of two or three syllables that form a pattern in a line of poetry. One of the most popular uses of the iamb in poetry is called iambic pentameter, in which each line of a poem contains five iambs. Almost all of the works of William Shakespeare, John Milton's Paradise Lost, and many poems by Elizabeth Barrett Browning are written in iambic pentameter. The iamb is used frequently in other poetic meters, such as iambic trimeter, which is a line of verse containing three iambs, and also appears in poems with mixed meter.
Many words form a natural iamb, such as today, request, and duvet, but an iambic foot can also contain two separate words or two syllables from different words. The iamb is one type of metrical foot that is used to study poetry. Most of the time, when analyzing a poetic work, one of the first steps is to identify the type of verse being used. The type of meter is determined by the number of feet in a line. The feet may be iambs, but may also be trochees, which also consist of two syllables, the first stressed and the second unstressed. A pattern of two stressed syllables in a row is called a spondee, and two unstressed syllables together are called pyrrhic.
After identifying the use of iambs or other types of poetic feet, the next step is to look for a pattern of syllables being used in each line, which is called the meter. Some poems have the same number of feet in each line, while others may use alternating patterns or no pattern at all. Possibly the most well known use of the iamb is in the meter known as iambic pentameter, in which there are five iambs in each line of a poem. These lines can rhyme but can also be unrhymed; unrhymed iambic pentameter is also called blank verse. Many of Shakespeare's plays are written in blank verse, but the pattern can often be difficult to recognize unless it is read aloud and the rhythm can be more easily heard.
There is some debate over the purpose of the iamb and other types of meter in poetry. In Shakespeare, iambic pentameter and other types of rhythmic meter are often used during main characters' soliloquies or when very important speeches are being made. In general, use of iambic feet may give a more formal feeling to a work of poetry and is often employed in older poetry. More modern poets often prefer to write in free verse, in which the pattern of meter and feet is random and more closely follows natural speech.