The style of the late 50s, engineered by Horace Silver, Art Blakey, etc. Still essentially Bebop, the style used hard-driving rhythmic feel and vehement, biting lines and harmony drenched with urban blues, rhythm 'n blues and gospel. Original compositions were stressed over the old standards used in Bebop, ranging from simple riff-based blues to elaborate compositions, sometimes using whole-tone scales. Hard Bop had a black, street flavor, a reaction, in part, to the intellectuality of the Cool School.