<P> Classical Chinese poetics, based on the tone system of Middle Chinese, recognized two kinds of tones: the level (平 píng) tone and the oblique (仄 zè) tones, a category consisting of the rising (上 sháng) tone, the departing (去 qù) tone and the entering (入 rù) tone . Certain forms of poetry placed contraints on which syllables were required to be level and which oblique . </P> <P> The formal patterns of meter used in Modern English verse to create rhythm no longer dominate contemporary English poetry . In the case of free verse, rhythm is often organized based on looser units of cadence rather than a regular meter . Robinson Jeffers, Marianne Moore, and William Carlos Williams are three notable poets who reject the idea that regular accentual meter is critical to English poetry . Jeffers experimented with sprung rhythm as an alternative to accentual rhythm . </P> <P> In the Western poetic tradition, meters are customarily grouped according to a characteristic metrical foot and the number of feet per line . The number of metrical feet in a line are described using Greek terminology: tetrameter for four feet and hexameter for six feet, for example . Thus, "iambic pentameter" is a meter comprising five feet per line, in which the predominant kind of foot is the "iamb". This metric system originated in ancient Greek poetry, and was used by poets such as Pindar and Sappho, and by the great tragedians of Athens . Similarly, "dactylic hexameter", comprises six feet per line, of which the dominant kind of foot is the "dactyl". Dactylic hexameter was the traditional meter of Greek epic poetry, the earliest extant examples of which are the works of Homer and Hesiod . Iambic pentameter and dactylic hexameter were later used by a number of poets, including William Shakespeare and Henry Wadsworth Longfellow, respectively . The most common metrical feet in English are: </P> <Ul> <Li> iamb--one unstressed syllable followed by a stressed syllable (e.g. des - cribe, in - clude, re-tract) </Li> <Li> trochee--one stressed syllable followed by an unstressed syllable (e.g. pic - ture, flow - er) </Li> <Li> dactyl--one stressed syllable followed by two unstressed syllables (e.g. an - no - tate, sim - i - lar) </Li> <Li> anapest--two unstressed syllables followed by one stressed syllable (e.g. com - pre-hend) </Li> <Li> spondee--two stressed syllables together (e.g. heart - beat, four - teen) </Li> <Li> pyrrhic--two unstressed syllables together (rare, usually used to end dactylic hexameter) </Li> </Ul>

Describe the concept of poetry in your own words