What is Diatonic Anyway?

Jazz guitarist Leon Rodriguez explains ‘diatonic’ in this music theory lesson specifically for guitarists.

When most of us get our first guitar lesson here in the USA, we learn the Blues scale or the minor pentatonic scale because our cultural music is largely based on the African American contribution to our American songbook canon. Those scales are six and five-note scales respectively. And that is great and essential knowledge for any musician and guitarist, an important sub-topic that we’ll definitely get into. However, what we are going to learn here first is based on what grew from what Pythagoras found out about the physics of music about 2,500 years ago. We’ve never stopped adding to it. It’s become the language, science, and craft of music itself. A system that explains ALL music including the Pentatonic system. The system we are going to learn is called the DIATONIC system. 

Diatonic means two tonalities. Each ‘Tonality’ is 4 notes long. The 4-note pattern we will focus on now is called a Major Tetrachord. The Interval between the 1st and 2nd note is a whole tone or 2 frets. The interval between the 2nd and 3rd note is also a whole tone or 2 frets. However, the interval between the 3rd and 4th notes is a half-step or 1 fret. The interval between the 1st note and the 4th note is a Perfect 4th or 5 frets. The same pattern of intervals begins again a whole step or 2 frets above the 4th note, beginning a whole new tonality or tetrachord, an interval of a 5th above the root of the previous Tetrachord. 

This continues in a Cycle of 5THs which we will discuss at length soon. It is in fact the interval of a Perfect 5th that is the core of the major scale, being the first audible distinction from the fundamental frequency of the overtone series that Pythagoras defined. The two adjacent tetrachords in sequence compose a series of tones we call THE MAJOR SCALE. This scale is the core of music theory. 

When we play the two tetrachords along one string, we can hear the sound of the Major scale while exposing the symmetry of the double pattern that begin at the 1st and 5th notes of the scale. Naturally, that’s not such a practical fingering for melodic playing, but it is for understanding it. Let’s apply our tetrachord to string pairs. 

The above string pair major scales deliberately avoid the half step interval shift between the 2nd and 3rd string. If you can add a vision of this string pair set, {65}, {43}, {21} regardless of what you play on the string pair, you can dependably retain identical fingering on each string pair because the interval between the even-numbered string is symmetrically identical to the odd-numbered string in the string pair, a perfect fourth. We’ll see this again and again and use it. 

At first, if you will slide the 1st note to the second note in the tetrachord with your 1st finger, palm muting with the right hand as needed, you can finish playing the rest of the tetrachord with a 1-3-4 left hand from a comfortable 4 fret range and keep to a “one finger per fret” general standard which I would strongly advise as a habitual organizing tool although nothing can or should be absolute in guitar playing. 

Any two of these adjacent string pair tetrachords played in sequence is a major scale. Remember the proximity of the 1st to the 5th in each string pair. Do to Sol. This is our first exposure to the cycle of 5ths! 

One of the most valuable things about this lesson is this visual that exposes how the theory presents itself. It is indeed a visual reference to the design of our instrument. That’s a big deal in the grand scope of things. 

Jazz Guitar Today: Thanks again Leon!

To be continued…Books and On-Line Private Lessons available at www.LeonRodriguezGuitar.com/shop 

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