The Language of the Diatonic Guitar

Sources of confusion in any endeavor must first be identified before the confusion itself can be dealt with. If you find the guitar fret board confusing; why? If you are confused by basic western music theory concepts, then it's likely that same confusion will make its way into your study of the guitar.

You may think that the concepts and terminology of music theory are too difficult to bother with, but remember that — in the western diatonic system of music, which is what you are working with if you play the guitar (whether you know it or not) — fundamentally there are only 12 major keys and only 7 notes in each key. Think of it like the 12 months of the year and the 7 days of the week. These are not huge numbers.

The following terms are essential concepts in diatonic theory;

Tonic, Supertonic, Mediant, Subdominant, Dominant, Submediant, Leading Tone

... They are the Scale Degrees. They are, more or less, equivalent to the following;

Do, Re, Mi, Fa, Sol, La, Ti ... 

I, II, III, IV, V, VI, VII ...

C, D, E, F, G, A, B ...

Here are simple definitions;

Tonic -  The tone upon which a key is based. Note number I. C in the key of C major.

Supertonic  - The tone a whole step above the tonic. Note number II. D in the key of C major.

Mediant - The tone a third above the tonic. Note number III. E in the key of C major.

Subdominant - The tone a 4th above the tonic. Note number IV. F in the key of C major.

Dominant -  The tone a 5th above the tonic. Note number V. G in the key of C major.

Submediant -  The tone a 6th above the tonic. Note number VI. A in the key of C major.

Subtonic - The tone a minor 7th above the tonic as well as the same note a whole step below the tonic. Note number bVII. Bb in the key of C major.

Leading Tone -  The tone a major 7th above the tonic as well as the same note a half step below the tonic.  Note number VII. B in the key of C major.

Notice that there are two 7ths; the Subtonic and the Leading tone. The importance of this distinction becomes clear, for instance, when you switch from playing a major key love ballad or folk song to playing a raunchy blues based riff. The major 7th (Leading Tone) is the norm outside "blues based" music, whereas the Subtonic is the norm in blues. This is a gross simplification, but it should illustrate the concept.

Hierarchies ... The Tonic and the Dominant are the landmarks in the system — Roman numerals I and V, respectively. You are already familiar with these two tones. Play any typical major barre chord, G major rooted on the 3rd fret of the 6th string, say. 

The lowest pitched note is the root of the chord, the next note up in pitch is the 5th. If you are in the key of G this G barre chord will the the Tonic Chord and the root and 5th of the chord will also be the Tonic and Dominant tones of the key.

If you play a G7th by releasing your 2nd finger and moving your 4th finger to the 6th fret of the 2nd string, you are playing what is also known as a "Dominant 7th" chord. This is not the same as a "Major 7th" chord. The difference between the G major, G Dominant 7th (usually referred to as G7th) and the G Major 7th chords is seen in the diagram which follows;

Each of the chords above have their own story to tell about where they come from and how they like to be used.

G Major chord


G Dominant 7th chord


G Major 7th chord



The G Major chord is a triad. It comprises three tones: G-B-D,  though there are three instances of the Root (G), two 5ths (D)  and one 3rd (B) amounting to six notes. This chord could be the Tonic chord in the key of G, the Subdominant chord in the key of D, or the Dominant in the key of C. When a 7th is added to the triad, it will be either a G Major 7th or a G Dominant 7th depending on which key degree it is positioned.

If a 7th chord is rooted on the Tonic (I) or the Subdominant (IV) it will be a Major 7th chord. If it is rooted on the Dominant (V), then it will be a Dominant 7th chord. This is true in every diatonic major key. It works this way because of the distribution of major and minor thirds within the key;

Study the diagram above carefully. Notice that the I and IV chords have the same interval structure of major and minor 3rds. Notice how the interval structure of the V chord differs from the I and IV.

The remaining chords are three "Minor 7ths" (ii, iii and vi) and a "Minor 7 flat V" (vii) — also known as a "Half Diminished" chord. 

Here are the 7th chords of the key of G major;

And here are the 7th chords of the key of D major;

The structure of each chord is actually only a starting point. For instance; although the I and IV chords are the same internally, their different positions in the key will potentially lead to differing harmonic and melodic possibilities when improvising around each of them. 

All contents of this blog are © Mark Newstetter