vi–ii–V–I

[1] It is "undoubtedly the most common and the strongest of all harmonic progressions" and consists of "adjacent roots in ascending fourth or descending fifth relationship", with movement by ascending perfect fourth being equivalent to movement by descending perfect fifth due to inversion.

[2] For instance, in C major, the chords are Am–Dm–G–C, which have roots that descend by perfect fifth (or ascend by fourth), as shown below.

[5] The progression is often used[6] as a turnaround, occurring as the last two bars of a chorus or section.

[9] The circle progression is commonly a succession through all seven diatonic chords of a diatonic scale by fifths, including one progression by diminished fifth, (in C: between F and B) and one diminished chord (in C major, Bo), returning to the tonic at the end.

[2] The ii–V–I turnaround lies at the end of the circle progression, as does the vi–ii–V–I progression of root movement by descending fifths, which establishes tonality and also strengthens the key through the contrast of minor and major.