I need a little guidance about learning the minor scales in 7 positions/patterns on a guitar. To begin with, I am reasonably comfortable with the major scales played in all 7 positions/patterns (covering the successive 7 modes?).
As per my comment, I wasn't quite sure what you meant there. Now I've watched the video, I think the video itself is where the confusion comes from!
Here, the video calls the notes A, B, C, D, E, F♯, G... "G major scale pattern 2". I think I'm agreeing with Tim's post here when I say that that's an unconventional thing to call those notes played in that order, starting on A. I would say he's playing A Dorian - the second mode of the G major scale, with the same notes as G major, but starting on A. That wouldn't itself usually be called playing a 'major scale' in a 'learning the scales' context, where there is a strong convention that you start (and end) on the root note.
If you don't agree that a scale should start on the root note, then I guess what the video says is fine. But generally the mental steps you need to take to play a particular scale (such as A major, or C major) is locate the root note (A, or C) first, then base your pattern on that.
However you learn your patterns, you need to be very aware of where your roots are. The whole point of a scale from a musical perspective is that it is defined by a set of intervals from the root; that's what gives a piece of music a certain flavour when you construct it from that scale.
From the theory standpoint, I am given to understand that the 6th mode (i.e. 6th position of a major scale is the (first?) position of a minor scale?
I wouldn't use the word 'position' how you use it there, but yes - you could call the 6th mode of the major scale the natural minor. Personally, as I've said in my answer to Flavor of the modes in melody, I don't like to think of the modes as coming from a major parent scale - I think of the diatonic scale (i.e. the note pattern, without any particular root) as the "parent" concept, and then of major/minor tonality and modal tonality as both being concepts derived from that.
Now I would like to learn the minor scales.
First can I just double check that you know how to play particular major scales first, by identifying the root on the fretboard, and playing the major scale pattern based on that root? For example, The way I would play an A major scale would be to:
- find an A note on the fretboard
- play the major pattern scale, starting with that A note as the root
tweaking one of the diagrams from the video, that's:
Note that we've started on A as the root (fret 5 on the low E string), and then played finger patterns that are the same as pattern 1 in the video - because pattern 1 in the video is the major scale pattern starting on the first string.
Another way to play it that's less of a stretch:
That's just another way to play the A major scale starting on the low E string. Note the roots circled in red.
Once you get to the point where if someone asked you to play "A major", or "B major", or "D-flat major", you could do it instantly, it should be just as clear what you have to do to play any natural minor scale - identifying the root on the fretboard, and playing the natural minor scale pattern based on that root. You can think of that minor pattern as being the "pattern 6" you were taught in that video, if that helps you; personally I prefer just to think of it as 1, 2, ♭3, 4, 5, ♭6, ♭7, 8, and then spot those intervals from my root (as suggested in Would it be a good idea to memorize relative interval positions on guitar?). It saves me from having to spend any more time learning scale shapes.
It might be that you've already started to think of things in the way suggested in that video, in which case my advice here might not make much sense to you. I can see that there are other sites on the internet that basically agree with what that video says, but I think it's confusing. If it wasn't, you wouldn't be here asking this question!
Now, coming to the E minor scale, my understanding after reading your answer is that I can use the same 7 G major scale positions to play E minor scale with the only difference being that the start and the end of the E minor scale has to be with the note E in that pattern?
If you agree that an E minor scale should start on E, then it doesn't make sense to think of what's shown in the video as "7 G major scale positions", because only one of the patterns shown in the video starts on G.
For what it's worth, I think a better way to describe the content of that video would be that it's teaching you 7 patterns of the diatonic scale - i.e. the diatonic scale starting at different points, each of which corresponds to one of the modern modes, the first of which (Ionian) is basically the same thing as the Major scale.