J. S. Bach frequently uses stretto throughout both books of his Well-Tempered Clavier (1722, 1740). Kathryn McDonald investigates the use of stretto throughout the Well-Tempered Clavier. Her main focus is on the frequency and density of stretto sections, without giving much emphasis to the harmonic function.

This paper will expand on McDonald's work with a further analysis of the harmonic function of Bach's stretto in his Well-Tempered Clavier. I define four harmonic functions in stretto passages: tonicization, modulation, prolonging single harmonies, and prolonging key areas. Through my analysis, I have found that Bach mainly uses stretto to prolong key areas, followed closely by modulation. In Book One, he also employs stretto for the tonicization and prolongation of single harmonies, a technique not present in Book Two. The data found shows that the tonic key is prolonged most often, while Bach tends to use stretto to modulate to either a tonic or predominant key.

The harmonic functions identified in this analysis suggest that there is a function of stretto beyond the "effect of greater intensity" described by Christoph Neidhöfer and Peter Schubert and the "increasing of tension" described by Robert Gauldin. Further research and analysis of other works is required to determine if these harmonic patterns are present in other fugues from the same period.