View post (harmonic minor sweeps?)
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In each key, there are 7 different triads you can build off the 7 different notes in the key. The roman numerals refer to which note you're building the triad off of. In a major key, the triads you build are I ii iii IV V vi vii(dim). Uppercase is for a major triad, lowercase is for minor. When you build triads off different scales, you end up with different chord patterns.