Tetrachords: The easier way to remember and understand scales

Tetrachords (in 12 TET)
The building blocks of scales
How the scales are built
Easy way to remember scales

A tetrachord is a set of four notes. Heptatonic scales like major scale or minor scale are made of seven notes and if you include the octave you have eight notes. So two tetrachords can be joined to make a heptatonic scale. 

In twelve tone equal temperament the octave is divided into twelve notes that are placed evenly along the octave. The interval between two notes next to each other is called a semitone. So the octave is made of twelve semitones. These twelve semitones can be divided to the lower and the upper tetrachord. 

Four notes have three intervals between them. We can display the length of intervals as semitone steps. Major tetrachord is made of intervals with semitone steps two two and one. 

Major scale is made of two major tetrachords. The lower tetrachord starting from the tonic and the upper tetrachord ending in the octave. In between is left two semitone steps. 

Major is also called Ionian and if you make a new scale out of every note of Ionian scale you get Ionian modes. These modes are seven scales that are built from four different kinds of tetrachords: Ionian, Dorian, Phrygian and Lydian. These are also known as Major, Minor, Upper minor and Whole Tone tetrachords. Ionian modes are also called Diatonic scales that are listed here. And you can also make Melodic scales from the same tetrachords. 

Another popular tetrachord is the harmonic tetrachord. And for the next list of scales I also present the Hungarian minor tetrachord and the Hungarian major tetrachord. Here is a list of multiple scales made with the harmonic tetrachord. 

And finally here I made a list of twelve tone equal temperament tetrachords that do not exceed six semitone steps. The names for the tetrachords are mainly based on the scale that is made by joining two similar tetrachords. There are also some common alternative names that are based on the upper or the lower tetrachord of a popular scale. Other than the traditional scale names are mainly by William Zeitler who listed and named all the scales in the website AllTheScales.org.