Aside from hip-hop's political and social undertones, it is, from an aesthetic point of view, a legitimate art form. Despite hip-hop's entanglement with popular culture, and so called "low brow art," aesthetics lies at the heart of hip-hop. Hip-hop wouldn't be hip-hop without its preoccupation with aesthetic form. This is what defines it. From the use of samples and drum machines, to its conversational and poetic verses, hip-hop has found its aesthetic niche in the world of art. Aesthetic form is largely how this genre of music forged its own identity, and because of this, hip-hop is aesthetically unique. When you hear hip-hop music there is generally very little contention over what genre of music it is.
One aspect of hip-hop's aesthetics is that it is traditionally a sample-based music form. Sounds and melodies are taken from previously published music, and are distorted, chopped up, and looped to create new melodies, essentially recycling music to create new music. This aesthetic form closely resembles collage art, where pictures and images are taken and reconfigured to create a new work of art.
Hip-hop has also defined itself aesthetically, by means of its distinct lyrical sound and structure. Rather than closely following musical tradition, where lyrics are predominantly sung, hip-hop's vocals more closely resemble that of spoken word poetry. More value is placed on intonation and rhyme schemes, rather than pitch, key and vocal fluidity. Despite breaking from musical tradition, hip-hop has defined its own aesthetic identity, and has incorporated poetic form into its music.