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Seven chords run every key
Take the seven notes of a key and stack them in thirds, and you get seven chords. Those are the diatonic chords: the only triads built entirely from the notes of the key. In C major they are C, Dm, Em, F, G, Am, and Bdim. In A minor they are Am, Bdim, C, Dm, Em, F, and G. Same notes, different starting point, different chord roles. Every song in a key is mostly built from these seven chords, with visitors from outside the key appearing only for special effect. Learning the seven chords of a key is therefore the fastest route to playing songs by ear, writing progressions that sound right, and understanding why some chord changes feel inevitable and others feel surprising.
Each chord has a Roman numeral and a function. In major keys the pattern is always the same: I is major, ii is minor, iii is minor, IV is major, V is major, vi is minor, and vii is diminished. The functions group them into three families. Tonic chords (I, iii, vi) feel like home. Subdominant chords (ii, IV) feel like a step away from home. Dominant chords (V, vii) feel like tension that wants to resolve back home. That is the whole drama of Western harmony in one paragraph: home, away, tension, home again. In minor keys the pattern shifts: i is minor, ii is diminished, III is major, iv is minor, v is minor, VI is major, and VII is major, and the dominant family is weaker in natural minor, which is why minor-key songs so often borrow a major V chord from outside the natural scale.
How to use this diatonic chord chart
Choose a key and a mode, and the tool lists all seven chords with their Roman numerals, notes, and functions. Start with C major, because the pattern is easiest to see without sharps or flats, then move to a key you actually play in, such as G major or E minor. Play the seven chords in order on your instrument. Listen to how the major and minor chords alternate, and notice the diminished chord at the end: it sounds tense and unfinished, which is exactly its job. Then play them out of order. Try I, vi, IV, V, the most used progression in popular music, and hear how the functions guide the ear: home, a softer home, a step away, tension, and back home.
The chart also teaches transposition. The Roman numerals stay the same in every key, so a progression written as I, V, vi, IV in C major (C, G, Am, F) becomes G, D, Em, C in G major and D, A, Bm, G in D major. If you learn songs as Roman numerals instead of chord names, you can play them in any key a singer needs, which is a genuinely employable skill. Bands transpose constantly for vocalists, and the musician who thinks in numerals transposes instantly while everyone else is rewriting chord charts. Use this tool to convert a song you know into numerals, then rebuild it in a new key and check your work against the chart.
Seventh chords and beyond
Each triad can grow a seventh note, still diatonic, and the pattern of seventh chords is just as regular: in major keys, Imaj7, iim7, iiim7, IVmaj7, V7, vim7, and viim7b5. The dominant seventh, V7, is the star of the set, because its tritone interval creates the strongest pull back to the tonic in all of harmony. If your progressions sound plain, try turning the V chord into a V7 and hear the difference. The progression analyzer will confirm which of your seventh chords are diatonic and which are visitors. Master the seven triads first, then the seven sevenths, and you will own the harmonic vocabulary of any key you choose to learn.
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