Online lessons - "Understand music theory"

ToneControl

https://www.understandmusictheory.com/

some is free, not sure if  it's great or not

and the related blog:
https://www.understandmusictheory.com/wordpress/

viz

It's really clear, and I like the way the whole approach is founded on musical staves and the layout of the piano, rather than, say, trying to illustrate everything on the guitar. I think it would be helpful to anyone trying to understand music. 

Teetonetal

viz said:

It's really clear, and I like the way the whole approach is founded on musical staves and the layout of the piano, rather than, say, trying to illustrate everything on the guitar. I think it would be helpful to anyone trying to understand music. 

Agree, a basic understanding of Piano makes learning music theory so much easier, it's a lot clearer visually than using guitar boxes.

I've often wondered if the way Guitar gets taught using Tab and Chord boxes is actually a real stumbling block in theoretical development as it stops you learning the notes, you end up doing everything from muscle memory and visual clues. Yet knowing the notes is an integral part, even the most essential part of any theoretical concept you want to learn.