What's the difference between a chord progression and a riff?

A riff is a melodic figure repeated over and over. Like Smoke on the Water riffs and Whole Lotta Love riffs. It's also called ostinato.

A chord progression is a series of chords that aim for establishing a key (as opposed to chord succession, which does not aim for it). These chords can be, however, expressed not only as straight-out strummed/played chords (like in many folk revival songs or some jazz etc.), but also differently, for instance in the form of a riff. http://www.theguitarmule.co.uk/shopimage… As you can see here, the riff of the first bar establishes the harmonic function of the tonic (in fact not necessarily a tonic major-minor seventh chord as written in the example).

In the fifth bar this riff is transposed up a fourth so it establishes the harmonic function of the sub-dominant. And then it's moved back to the tonic and then to dominant etc. more.

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