How can I deduce in which scales and mode to play?

Question

This is maybe a naive question.

Often, guitar tabs are given as a succession of chords (and/or a melody).

Is there a method to know systematically in which scale and/or mode can I play?

Maybe this could be illustrated by these chord change:

Bm - D - F#m7 - E

Answer 1

With tabs you need to know some theory first on how to determine the key by the chord progression. A quick and simple way to do this is to find the first and/or last chord of the song. But learn I - IV - V twelve bar blues and how to solo with pentatonics first before hitting the modes. You need to understand basic theory before you get into anything beyond a Pentatonic scale. Your example chord progression is more complicated then a typical pop or blues song. Although it starts on Bm it can be thought of a B Dorian progression.

Your chord example with the notes are:

Bm = B D F#

D = D F# A

F#m7 = F# - A - C# - E

E = E - G# - B

Those notes from these chords would be in A Major/F# Minor key:

A B C# D E F# G#

Modes derived from scale:

• A - Ionian (Major)

  B - Dorain

  C# Phrygian

  D - Lydian

  E - Mixolydian

  F# - Aeolian (Minor)

  G# - Locrian

Modes that can be played over the chords:

• Bm - B Dorian

  D - D Lydian

  F#m7 - F# Aeolian (Minor)

  E - E Mixolydian

Try Bm Pentatonic Scale to solo with first

B D E F# A

Answer 2

You ask for a systematic method. If there is only tab to follow, unless you know all the note names on guitar, it's difficult. When the music is there too, it's easier, provided you can name the dots.

Make a list of all the notes used, not including the accidentals with a #, b or natural before them. There should be 7, but not all notes are used in every song. See TTSTTTS to find the missing one or two.Put them in order, in a circle works best. Find the first note of the major scale they belong to. This is the one that gives a clockwise spacing of T T S T T T S between notes. T=2 frets, S= 1 fret. When you've found that note (A in the example above), you've found the major key.

When you've learnt the modes, you'll know that the 1st note is the start of Ionian, 2nd Dorian, 3rd Phrygian, 4th Lydian, 5th Mixolydian, 6th Aeolian, and 7th Locrian. Since the tune you mention is based around the B, the 2nd note, you can use Dorian.

You may notice that all the above 'belong' to A major, and all play the same set of notes, albeit with different tonal centres. E.g. E Mixolydian uses the same notes as A Ionian (major).

This may appear complex, but after doing it with lots of songs, it becomes easier. You'll probably find more songs in maj. (Ionian) or minor (Aeolian) than the others, depending of course on genre.