Confused about altered and extended guitar chords? Here’s the theory behind them – and how they can supercharge your songwriting

Jimi Hendrix plays London's Royal Albert Hall in 1969, and is lost in the moment as he plays a rhythm figure on his Fender Stratocaster.

Terms such as ‘altered’ and ‘extended’ chords are relatively simple to explain. Extended chords add other notes from the scale to the existing root-3rd-5th triad (for example, C-E-G), so if we add a 7th, we’d call this a major 7th chord (C-E-G-B).

We can extend up to a 13th in this way by progressively adding in the non-chord tones of a scale – in theory, at least.