Jarkko's reply is right. Thanks for jumping in, Jarkko!

Originally Posted by: kk4joq

Suppose I am in the key of G and I wish to play in dorian mode.

[p]Modes can be confusing. And the 2 different possible explanations you posted are a good example of why!

In general, there are 2 ways of looking at modes & you have to specify which one you mean.

1. Structural: each mode relates to a parent scale. So you are always in G major, and the various modes are just ways of playing the G major scale, but starting on each note in turn. Often this is used to stay in one key, but play over the chord changes within the key.

2. Ornamental: You just play whichever mode you like the sound of at the time regardless of the key. This requires that you know & apply the scale or mode interval formula.

I have 2 tutorials on modes that cover both of these approaches in detail.

https://www.guitartricks.com/tutorial.php?input=370

https://www.guitartricks.com/tutorial.php?input=770

Hope this helps! Have fun with modes!