How to Find the Key of a Song on Guitar
Knowing a song's key is useful for several things at once - from picking a pentatonic position for a solo (see [[connecting-scales-and-chords:the article on connecting chords and scales]]) to figuring out chords by ear. You can find it without trained musical ears, using a few practical signs.
Sign one: the last chord of the song
The final chord often matches the tonic and is therefore a useful first hypothesis, but it is not a rule: a song may end on another chord, stop unresolved, or modulate. If the final chord is Am, test A minor as a possible center, then confirm it from the melody and the full progression.
Sign two: the chord that feels like it wants to be the last one
A chord that sounds like 'home' and gives a sense of resolution is a strong tonic candidate. In modal music, blues, looping progressions, and harmonically ambiguous songs, however, the center may not be obvious at first. Check that impression against the melody, bass, and recurring cadences.
Relative major and minor share the exact same chords
A major key and its relative natural minor use the same diatonic notes and triads; C major and A minor are the standard example (see the article on CAGED). Minor-key music often raises scale degree seven and uses a major dominant chord, though, so the chord list is evidence rather than a complete answer. Confirm the center from melody and resolution.
Sign three: the full list of chords in the song
Write down every chord and find the key that explains most of them (see the article on ten chords). A chord outside that set is not necessarily an error: it may be a secondary dominant, modal borrowing, or a modulation. Consider not only the chord list, but where each unusual chord resolves.
Why the key matters in practice
Once you know the key, it's immediately clear which pentatonic position or scale to play over the accompaniment for a solo (see the article on getting started improvising), instead of hunting for notes one at a time. This isn't a theory exercise - it's a direct practical shortcut into improvising.
Pruébalo en la práctica
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