Nexus System ❷Classification

In the previous session, we explained the general overview of the concept of chord ‘nexus’. The musical ideas brought about by the connection of two chords become even clearer when analyzed through two ‘control factors‘: the change in the root and the change in chord quality, in addition to the TDS functional theory.

While you’ve already got a basic understanding of chord quality through discussions in the ‘Quality Change‘ session, we have not delved much into the movement of the root.

The ‘movement of the root’ is referred to as Root Motion. From here, we will learn how crucial it is to understand root motions.

1. Classify by Root

We will now examine each of the 30 different nexus patterns individually. However, it is done not in the form like “V chords progress to…,” but rather based on the movement of the root as the primary criterion for classification, such as “root moves by a second” or “root moves by a third”.

Traditional classical/jazz theory books also adopts such methods, for these genres have preferences for specific root motions (some of the motions are very frequently used, while some are scaresely used).

And though it’s not explicitly theorized, even in contemporary genres like rock and EDM, have likings and tendencies for specific root motion patterns.
Hence, by classifying nexuses by root motion, we can acquire highly practical wisdom like “use this motion for jazz feel”, “this is an EDM style modern progression” etc.

2. Define Stuffs

Before getting into detailed explanations, I’d like to define a few things to keep text clear.

Symbols for “Ascend” and “Descend”

From this point forward, you will come across phrases like “ascending by second” or “descending by third” sooooo frequently. To simplify these, I will use triagnle symbols such as 2^▲ 3_▼ for abbreviation.

In essence, it’s similar to writing “A minor” as “Am”. Regarding pronunciation, I’d like to leave a little room for personal preference. For instance, for 5^▲, you can call it 5 up / fifth up / fifth above / up by fifth / ascend by fifth and so on.

Ignoring Octaves

For example, in the nexus V→I, the movement of the bass can either be “up by fourth” or “down by fifth.”

However, when discussing chord progressions, the octave difference is entirely irrelevant, so we treat these as equivalent. By doing so, the connections between the six prime chords is categorized just to three types, namely, second, third, or fifth.

Why specifically use “fifth” instead of “fourth”, why go with the larger number? One reason is that this is simply a convention strongly present in music theory realm¹.

Another practical reason is that it makes memorization somewhat easier when dealing with all these connections (explained later).

It might feel a bit uncomfortable that the numbers skip, but considering that 2, 3, and 5 are the smallest prime numbers, you could even view them as more aesthetically beautiful than 2, 3, and 4!

Summing up the content so far, the connections between the 30 types of primary chords can be categorized into the following six types.

Treatment of “Prohibitions”

In contemporary music, there are no prohibitions on chord progressions. However, understanding what “used to be prohibited” holds significance. Adhering to these rules can lead to well-behaved music, while breaking them can result in avant-garde tracks. Essentially, it enables you to deliberately control the “modern/traditional” aspect of music.

Therefore, such “former prohibitions” are indicated with dashed lines of a different color, highlighting their special status.

Since these nexuses are often not extensively covered in theoretical texts, the LMT fills these gaps by explaining them based on collected examples.
Now, with the detailed analysis saved for late individual articles, let’s first broadly study the characteristics of each nexus type.