SUBSTITUTE
Not all chord progressions stay strictly within the diatonic/chord scale convention – and that’s a good thing. Taking a little look at the theory involved here, the C major diatonic/chord scale is Cmaj-Dmin-Emin-Fmaj-Gmaj-Amin-B diminished (Bm7 b5 is also commonly used). These are often numbered sequentially using Roman numerals,