What is metre in poetry, and what is iambic pentameter?
Metre is the organised pattern of stressed and unstressed syllables in a line — the underlying pulse a poem is written against. Iambic pentameter is the most common English metre: five iambs, an iamb being an unstressed syllable followed by a stressed one.
The vocabulary, which is simpler than it looks. A foot is one unit of the pattern. The common feet are:
Iamb — unstressed, stressed: a-BOVE.
Trochee — stressed, unstressed: GAR-den.
Anapaest — two unstressed, then stressed: in-ter-VENE.
Dactyl — stressed, then two unstressed: TEN-der-ly.
Spondee — two stresses together.
The second part of the name counts the feet: trimeter three, tetrameter four, pentameter five, hexameter six. So iambic pentameter is five unstressed-stressed pairs — roughly ten syllables — and blank verse is unrhymed iambic pentameter, which is what most of Shakespeare's dialogue is written in.
Why iambic pentameter dominates English. Not arbitrary convention: it sits close to the rhythm of ordinary English speech, which is stress-timed, and a line of about ten syllables is roughly what fits comfortably in one breath. It is regular enough to feel patterned and long enough not to feel sing-song.
The thing that actually matters: metre is the pattern the poem departs from. A perfectly regular line is rare and usually dull. Meaning is carried by the substitutions — a trochee at the start of a line to make it turn sharply, a spondee to slow it, an extra unstressed syllable at the end. The famous line about a question of being opens with an inverted foot and ends with a hanging eleventh syllable, and both choices do work.
Free verse abandons regular metre but not rhythm — it organises sound by other means: line breaks, repetition, phrasing.
Scansion is the act of marking the pattern, and reading aloud beats theory every time.