Understanding method of applying modes on chords

Question

I am learning about modes and trying to apply them on guitar over chord progressions, and I wanted to understand how exactly to know, when you hear some song, "ah, this song allows me to play Dorian in A over it, or Mixolydian in G over it", etc.

I found a method of determining this here, quote:

In the son.g Oye Como Va by Santana, we have the following chords: A Minor - D7 If you look at the Harmonized Major Scale, you'll see that this corresponds to a: ii - V, in the key of G Major. Since we're playing the G Major scale over a chord progression that's tonal center is A Minor, we know we are playing in A Dorian (The 2nd mode of G major is A Dorian).

Having this information, I tried to practice it, by applying it to other songs. I took for example "Fly Away" by Lenny Kravitz. The song has the chord progression:

A C G D

To my ears, it sounds like I should be focusing on the start of the progression which is A and C, since A sounds as tonal center of the progression (to my ears at least). So I opened up Harmonized Major Scale chart:

...and here is where I am stuck. If I look at the chart, the combination of A and C appears at:

• option A) "I III" in A, this would give A Ionian (?)
• option B) "II VII" in B, this means A Locrian (?)
• option C) "V VII" in D, so A Mixolydian (?)
• option D) "II IV" in G, so A Dorian.

I tried these assumptions and the A Dorian sounded really good (to my ears, subjective) on Fly Away. And this is where I get confused, because I feel like I chose the option totally randomly based on just occurrences in the harmonized major scale chart. So I guess the correct answer was: option D) with A Dorian, but why not the others too? Why are the other options wrong, did I misunderstood the method of identifying the right mode?

How do you know really know a mode fits in some key, when you see a chord progression?

Thank you.

Answer 1

This may well be perceived as a dupe - there are already lots of similar questions on this site.

However - you consider A Dorian. Let's look at the notes from A dorian. A B C D E F♯ G. The chords for the song are A C G and D. There's certainly a 1 and 3 from each of those chords in the whole mode - C&E, G&B, D&F♯, but it doesn't bode so well for the A- A&C gives Am. Which usually sounds fine in a Bluesy way over A major, so 'it works'.

You consider A Locrian - A B♭ C D E♭ F G. Lots of clashes there, but with Locrian, that's par for the course!(Read later).

You also consider A Mixolydian - A B C♯ D E F♯ G. Some clashes there too.

When a piece has only diatonic chords/notes it is easier to use one scale - the diatonic of that key. However, when a set of chords is not diatonic - A C G D is one example - then it'll be a sort of compromise to use one mode throughout. Better, maybe, to play with the changes. By using notes which work with a chord and the following chord, the transition can sound very smooth. Example: finish the A bar on an E note, and that could even be tied to the first part of the C bar.

And, as an aside - your Locrian isn't right. A Locrian has the parent key of B♭.

Answer 2

Completely agree with Tim above. In case a helper sheet may be of use, here is my mine listing the modes, keys and chords. HTH - catz