Modes!!

Sure thing.

What you show as a Dorian scale in the key of G is indeed Dorian, but it's not G Dorian - it's A Dorian. When you find the notes of a mode by starting from a related major scale, the modes you find start with the different scale degrees.

In other words, with the notes of G major you have:

G Ionian (or major) if you start from G
A Dorian if you start from A
B Phrygian if you start from B
C Lydian if you start from C
D Mixolydian if you start from D
E Aeolian (or natural minor) if you start from E, and
F# Locrian if you start from F#.

In the second approach you're not trying to find the Dorian mode related to G major (which is A Dorian) - you're trying to find G Dorian. For G to be Dorian it will be the second note of the major scale, so you move back to F, and from the F major scale you find these modes:

F Ionian (or major)
G Dorian
A Phrygian
Bb Lydian
C Mixolydian
D Aeolian (or natural minor)
E Locrian

Both explanations are correct. You're getting confused because you think they're describing the same thing, and they're not. In the first case you take a major scale (G) and you use it to find the related Dorian scale (A Dorian). In the second case, you're saying "I'd like to find G Dorian", and you're locating the related major scale (F major).

Modes are confusing. And most of the explanations are plain and simple rubbish. In my opinion, here's the best way to understand modes:

Lydian is the major scale with a #4
Mixolydian is the major scale with a b7
Dorian is the natural minor scale with a #6
Phrygian is the natural minor scale with a b2

Ionian is the major scale; Aeolian is the natural minor scale. If you should need Locrian, find the Phrygian first and then flat the 5th.

No matter what method you use, you're finding the mode through some other scale. In the methods you describe, you're finding G Dorian from F major, or A Dorian from G major. In my method, you find G Dorian from G natural minor. So no one method will be any faster than the others.

But the other methods will have you thinking in the wrong key!

If you're thinking "I'll play F major starting from G", you are thinking in F major. But if you think "I'll play G natural minor and raise the Eb to E natural", you are now thinking in terms of G... which means you have the correct tonal center to begin with.

For comparison's sake:

Your method #1: You want to play a Dorian using the notes from a G major scale. The second note is A, so you'll be in A Dorian if you "think" G major, but focus on A. You play A-B-C-D-E-F#-G-A, but you're thinking about G major.

My method: You want to play in a Dorian using notes from G major. Since A is the second note, you take the A natural minor scale and raise the sixth note. You play A-B-C-D-E-F#-G-A (the same notes as your method), but you're thinking in A minor. That makes it much easier to keep your focus on A.

The reason they are different is because they are relative to the context of what key you actually play those modes. If you were to play the Dorian starting on 'A' ('A' Dorian), it would be relative to the key of 'G'. Yet, if you were to play the Dorian starting on 'G' ('G' Dorian), it would be relative to the key of 'F'.

So to put it simply, if you were to play in the key of 'G' Major, you would use the 'A' Dorian mode, since all the notes in it originate from the 'G' Major scale.
But if you were to be playing in the key of 'F' Major, you would play the 'G' Dorian mode, because all of those notes originate from the 'F' Major scale.

Just the same, if you were in the key of 'C' Major, then you would use, not 'C' Dorian, but 'D' Dorian. The same goes for all the modes, if you were to use the Phrygian mode in the key of 'C', then it would be an 'E' Phrygian mode.

I hope this helps you understand :)

NoteBoat, I'm flabbergasted at your knowledge, not only here but in other threads as well. But I want to ask you about your method to figure out what notes should be played in certain modals.
How is it easier to play in your way than conventional method?? In terms of F major, Do you actually think "Ok, I'm playing G Dorian, so I'll play G minor with #6" and do you figure out the notes as you go? Unless I'm magically seeing all the notes on the fret board, I don't see it possible for me to play fast. Obviously I'm a mediocre and need to improve. Wouldn't it be easier to think that I'm playing F major but I will start and finish at F? Because I would just need to focus F notes in conventional method only instead of #6 in your method?
I have played guitar only for a year and I tend to invest more time on understanding theory than actually playing guitar lol. But music theory really interests me.

Yeah, I do think "I'm in G minor with a sharp six". It's really not hard to do, and if you know your basic major and minor scales cold it doesn't even take very long to get the hang of it.

If I'm in G minor, I know the #6 is E natural. I know where all the Es are on the fretboard, so it's pretty easy to visualize. And there are several ways you can go about "seeing" dorian (or any other scale) on the fretboard by relating it to the other stuff you already know. For example, if you know your melodic minor scale, that's the natural minor with a #6 AND a #7 - so you could just play that and lower the 7ths.

I recommend thinking in terms of intervals. Scales are made of intervals, and up or down changes the mode. For example, C major starting from the fifth as the new tonic* makes G major; starting from D makes D minor. And so on. Transposition dictates everything. This process also implies tonality, the circle of fifths, and relative major/minor keys.

*Initially I said root, but roots are only the lowest notes in root-position chords. Tonic is related to key.

For example, C major starting from the fifth as the new tonic* makes G major; starting from D makes D minor.

The notes of C major starting from the fifth make a G Mixolydian scale, and the notes of C major starting from D make a D Dorian scale.

Oh right, I forgot the sharps in those keys. Only C is major made of all naturals. The point is the same, though.