Poetry is the structural rhetoric used to evoke emotional qualities. Rap is, at the etymological root, the chanting of rhymed lyrics in time to a beat. The literary facet of poetry has been around for ages, long before the stories were translated into reading interpretations, while rap was used in many ancient forms of ritual and storytelling. In general terms, both are designed to move the listener or reader to a particular feeling.
Some of the most famed poets of our time, Elizabeth Barrett Browning, Langston Hughes, Maya Angelou, and others perfected the notions of rhyme, assonance, repetition and verse through well thought out examples of experience. Detailing the revolution of society, they were the witnesses to life's changes in the most beautiful and, sometimes, haunting of terms. Langston Hughes' "Life Ain't No Crystal Stair" is the proverbial foundation for what would later become rap songs like "The Message."
A few of the most eccentric and famed rappers of our time, Raekwon, Ice-T and Eminem represent the onomatopoeia and fast-spoken thoughts that have framed the evolution of rap over time. While many poems can be turned into a rap song, you'd be hard pressed to find Maya Angelou spitting the lyrics to "Cop Killer" a capella at some high society function, which speaks to the sociological separation between rappers and poets.
Artists that overlap this concept, both in theatrics and talent include, folks like the Old Dirty Bastard, who lived the qualifying poetic lifestyle of tragedy and comedy, while others like Mos Def use every breath as a public display of affection for the spoken word. Some could argue that Jay-Z, with his vocal dips, whips, and turns would creatively fare just as well in iambic pentameter as Shakespeare, or some other antiquated wordsmith.
To illustrate this point further, we've created a Venn Diagram showcasing the distinctions in rappers, the poets, and those who blur the lines faster than make-up on Britney Spears. Feel free to use the comments sections as your own poetic paradigm.