What is a "hemiola"?

A hemiola is a feature of music that originated in the Baroque period. It comes about in music in triple time when the composer subverts the metre by placing the stresses of the music in different places, specifically:Instead of the stresses being at the downbeats (imagine the music being one in a bar):1 2 3 | 1 2 3 | 1It momentarily changes to being every two divisions:1 2 3 | 1 2 3 | 1This almost always occurs at a cadence in the music where the resolution happens on the downbeat of the following bar (the final 1 in the diagram above). In all Baroque music in triple time, students should look out for hemiolas where they see cadences, and indeed if they see hemiolas should look for the corresponding cadence.