Modes is a concept that I think is overly clouded in mystery. First of you need to disregard the idea that the Major Scale is just one harmonic relationship. The Major Scale is in actuality seven different harmonic relationships. Let me explain further.
If you’ve already watched this ViHart video then you know that the brain perceives information like sound in an incredibly complicated way. Have you ever seen those color illusions where changing the “real” colors around an object changes how we percive the original object. This happens because we do not see every wavelength as a certain color but rather the brain partly interprets the visual colors based on many different visual inputs.
Now if we try to create an analogy for Modal thinking then we should view the major scale as a set of seven notes that each have their own specific Mode attached. The G-Major Scale consists of these notes in this order: G, A, B, C, D, E, F#.
If I play the scale starting on G and playing the notes in order to the G octave above (from the first note to the eighth) the brain perceives all the harmonies as intervals from the G root note. If I conversely start on the A note and end on the A note (the second degree of the scale) playing the notes in the same order from A to A then the brain perceives the harmony as the A Dorian harmony because we stack all the other notes up against the A note or the second degree of the scale. Many learn the modes as seperate un-related scales that each have their own soundscape. This is fine in itself but in my view a rather unconvenient way of learning the fretboard for practical use. So instead of remembering 7 different scales I view the Major Scale as a single scale with 7 different modes of playing.
The modes are broadly either a minor or major modes which is clearly defined by the third (a Flat third ♭3 for Minor). There are four Minor Modes within the Major Scale the Aolian (6th mode) being the true or typical Minor that we are used to playing and hearing. This is the reason why I do not teach the Minor scale as a seperate entity but rather as the 6th mode of Major.
A small case study: lets say that I’m playing the guitar on stage alone with a audience. If I want the audience to perceive my playing as a particular Mode (let’s stick with Dorian here) I need to accentuate the A note of the G Major Scale so that the brains of the people in the audience perceive the A note as the base to think about the intervals. Now let’s say that another guitar player steps on stage while I’m doing this awesome solo in A Dorian (you, the audience, perceive the solo as A Dorian because I’m letting the A note dominate the playing). Suddenly the second guitar player starts hammering out the G Major chord with some nice rhythm becoming my backing or rythm guitar essentially. What happens then is that even though I try to solo in Dorian (i’m accentuating the A note) you the audience start hearing everything I do as the G Ionian or Major scale because his chord the G Major becomes the base-note or reference that the brains in the audience use to define the harmony they hear. This is made clear in the video below which plays through the Major Scale seven times each time accentuating a different note in the scale.
To summerize: If you know the Major scale then you know all of the Modes found within it. It’s all a question of which note in the scale you decide is your root. If we accentuate the second degree it becomes Dorian, the third degree Phrygian and so forth. The Chart below explains the relationship in the Major Scale everything on the chart is a Formula except for the notes in the Major Scale they ofcourse depend on what key you are in. Everything I do on this page is in G-Major which has E-Minor as the 6th mode thus G-maj = E-min.