A concrete starting point
C–G–Am–F = I–V–vi–IV in C major
Three useful major-key frameworks
I–V–vi–IV becomes C–G–Am–F in C major and G–D–Em–C in G major. The diatonic turnaround I–vi–ii–V becomes C–Am–Dm–G. A ii–V–I sequence is Dm–G–C; seventh-chord versions such as Dm7–G7–Cmaj7 add voice-leading details. These are abstract chord patterns, not supplied copyrighted song melodies or arrangements.
Minor and blues need context
In A natural minor, i–VI–III–VII gives Am–F–C–G. A tonal dominant E major introduces G-sharp outside that natural-minor collection. A basic twelve-bar blues framework uses I for four bars, IV for two, I for two, V for one, IV for one and I for two, with many common variations. Dominant-seventh qualities on I and IV do not make those chords ordinary diatonic triads of one major scale.
Turn a formula into a practice task
Select a tonic deliberately, enter chord symbols in the Roman converter and check their degrees. Use the progression transposer to keep chord qualities while moving roots. Generate a short backing sketch and try a small original melody above it. The tools do not infer a song’s real key or choose an expressive arrangement. Keep your comparison to one change at a time.
Put it into practice
These examples describe explicit written notes and relationships. A diagram or generated phrase does not replace listening to a complete musical context, choosing a comfortable register or checking a physical technique with a teacher.