Let's take one string of the five-string bass to understand the principle of the diatonic mode construction. Look carefully at the picture, all seven diatonic modes are the product of the Natural Major mode. Every degree of the Diatonicism is a tonic for the corresponding mode. A method of this textbook is developed taking into account that our "music" ear is tonal. Having "tuned in" for any key, we can easily identify by ear notes which are in and out of this key. Therewith, a "tune in for the key" state is steady, you might say, that our ear, having "tuned in" for some key, made itself comfortable in it and refuse to leave it. Such peculiarity of our ear results, firstly, in, that our ear, being in a "tune in for the key" state, cannot hear (without special training) tones of another key, and, secondly, any note, out of the given key, strives to destroy our comfort sense of the key.
Seven diatonic modes
To know more about diatonic modes, let's examine each of these in one position, starting from the lowest string; it is E string in this case. This approach visually demonstrates the similarity and the difference between received fingerings.
Seven diatonic modes include: Ionian (Natural) major, Dorian minor (+6), Phrygian minor (-2), Lydian major (+4), Mixolydian major (-7), Aeolian (Natural) minor, Locrian minor (-2), (-5).
Fingerings of Ionian major and Aeolian minor are standard. Fingerings of other modes differ from standard ones with indicated alterations, marked with numbers. Signs plus (+) and minus (-) are often used instead of sharps (#) and flats (b) correspondingly in the contemporary chord notation. Numerals mark altered mode degrees. Such structure of the Diatonicism remains the same in any key and viewed alterations are called standard diatonic alterations. To identify the key, we have to choose the pitch of the main tone (the tonic) and detect the mode inclination (major or minor), that is to choose one of tonal centers of the Diatonicism. In other words, the structure of the Diatonicism is the structure of the key, we only have to choose the pitch of the tonic and one of the tonal centers. A triad consists of the first (I), the third (III) and the fifth (V) mode degrees. Basic diatonic alterations almost don't affect triad degrees, when building the triad on the basis of the diatonic modes, we get three major triads, three minor triads and one diminished triad on the seventh degree of the Natural Major or on the second degree of the Natural Minor. Thus, three different chord fingerings (a major triad fingering, a minor triad fingering, a diminished triad fingering) are enough to play all the scale in triads.
Seventh chords consists of the first (I), the third (III), the fifth (V) and the seventh (VII) degrees of the mode. Pay attention that the Mixolydian mode has an altered seventh degree, so we get one more application - the major seventh chord with the lowered VII (seventh) degree. It is called the dominant seventh chord, as it is built on the V degree of the natural major mode, which is the main representative of the dominant function in the mode. And the Half-diminished seventh chord or the minor seventh chord with the lowered V (fifth) degree is built on the VII (seventh) degree (the Locrian Minor) of the Natural Major. So, to play the full seventh chord scale, we have to know four different seventh chord fingerings. These are fingerings of: a major seventh chord, a minor seventh chord, a major minor seventh chord (dominant seventh chord) and a half-diminished seventh chord fingering. It is very important to understand the circumstance, that all fingerings are universal and the same in all keys.
As well as triads and seventh chords the pentatonic scale is built on the base of scales but on the other principle. Triads and seventh chords can be built on the base of any scale (except the chromatic one), and the pentatonic scale is built only upon the diatonic scales. The structure of the pentatonic scale is the result of the diatonic structure. Altered degrees in the major diatonic modes (the risen IV fourth degree in the Lydian Major and lowered VII seventh in the Mixolydian Major) are absent in the major pentatonic scale. In the minor pentatonic scale altered diatonic degrees are absent too. These are the risen VI sixth degree of the Dorian Minor and the lowered II second degree of the Phrygian Minor. So, we can play the pentatonic scale (keeping in the key) almost from any diatonic degree except the Locrian mode where the V fifth degree is altered too. The pentatonic scale returns us again to three different fingerings.