The first time you play a C#dim7\u2014such as the one in Ex. 1a\u2014you may find yourself wondering why you\u2019d ever need such a dissonant cluster of notes. Truth is, diminished 7s and other such strident grips are, ironically, incredibly useful for making progressions sound smoother. Plug that C#dim7 between C and Dm7 (Ex. 1b), and its jagged shape all but disappears\u2014like the last piece of a jigsaw puzzle. Get hip to its pungent sound; you\u2019ll start hearing it everywhere \u2014not just in jazz, but also in rock, soul, blues, and other genres. This lesson includes Power Tab and is featured on the following CD compilations: JAZZ U, ACOUSTIC U.