WHAT IS A SECTION?
A section is each of the elements that make up a song. In the next page we will see the most common types of sections. Some are very simple. Others only have a filling function. But some express ideas, with a well-defined beginning and end. We call these sections phrases and they are the most important part of a song. Let's now focus on them.
The composer of the piece builds each phrase in the same way that a poet creates the stanza of a four-line poem.
I eat my peas with honey;
I've done it all my life.
It makes the peas taste funny,
but it keeps them on the knife.
If someone recites this poem but stops at the end of any of the first three lines we will have the clear feeling that we need more information, that there must be more things to come. However, once we reach the end of the poem, the idea is complete. If you like you can then add more verses, but if not, the idea is complete in itself.
The same thing happens in music. If the musicians only played two or three eights, we would clearly have the feeling that they had left their job half done. Each of these complete ideas is called a phrase of a song.
Songs are made up of different sections, including phrases, and there are no rules saying just how many they should have or how long they should be.
Nevertheless, in swing music, the phrases usually last for 4 eights (8 bars), 6 eights (called 12-bar blues) or, more rarely, 5 eights (10 bars).
There are songs that have a single phrase which is repeated several times (called the AAA structure and in this case the phrases usually have of 6 eights, although this is not always true). Other pieces have several phrases which are combined in very different ways. The AABA and ABAC structures are examples of this, but there are many other possibilities.
What differentiates one phrase from another?
You may wonder why the phrases are called A or B. The answer is very simple from the outset: the first phrase after the introduction, will be called A. The following phrases, if they are the same as the first, will also be called A. If they are different they will be called B, C, and so on.
But when we say that two phrases are the same? Is it when they have the same lyrics? The same melody?
If you look at the example of 12-bar blues of the previous page, the first phrase (which we call A) and the second (which we also say is an A) have a very similar melody, but it is not exactly the same. You may doubt, therefore, whether the common factor is the melody. But when the third phrase (which we also say is an A) comes, in which the first solo enters, the original melody is completely lost. Therefore, it is not the melody or the lyrics. What all the phrases of this song have in common (and what makes us consider the sections as the same or different) is their harmony.
What is harmony?
We could say that harmony is the backdrop that every song has and which is determined (in most cases) by the succession of musical chords that make it up.
Harmony is as important as the melody and can be as decisive as in the following example. Pay attention to the way in which, keeping the same melody but changing the harmony (the accompaniment) completely changes the idea that the melody expresses:
On the other hand, there can be many melodies that fit into one harmony. But not all fit in to a specific harmony. In fact, this is what a musician does during improvisation: they use the same basis (same accompaniment and chords) to create a new melody that fits in, which binds, despite being quite different from the original melody.
In the next video you can see the succession of chords (marked with Roman numerals) of the song Undecided played by the guitarist.
This is achieved thanks to the fact that the Roman numerals tell the musician the relative musical distance there will be between one chord and another.
For example, if you want to play this piece in E major, this chord will be assigned, by agreement, the Roman number I. Since musicians already know that the fourth degree of E is A major, when they see a IV in the score they know that they must play the fourth degree of the E, that is the A. And so on.
If they want to play it in C major, the chords that would correspond to number IV would be F major and to the V a G major.
Anyway, now we do not need to know what the chords would be. It is only a question of you seeing how the sequence is repeated and how the A sections always begin with the reference agreement (designated with the number I) while the B sections begin with higher harmonical tension and, therefore, with a different chord (in this case number II).
Note that the chord progression is the same in all the A's and also between all the B's. Also notice that, from the point of view of the tension of the music, the B's represent a change in level (it may be useful to imagine that, when the song starts it is on the ground floor of that musical piece and that when the B arrives you are rising, tensely, to the first floor).
The following video has the same harmonious basis (the chords) but now the melody is added. In the first chorus the soloist plays the original melody while in the second and third chorus there is an improvisation (a solo).
It is quite normal that in this second video it is harder for you to continue to feel the chords and perceive the harmony. Nevertheless, the chords are there, and both the original melody and the solo fit perfectly to the harmony. Train your ear, listening to a lot of music can help you to perceive it. At the end of this section about the structure of the songs you will find examples that will allow you to practice all this.
As a strategy, while listening to and analysing a piece, if you want to try to find out which phrase you are in you can try the following: memorize the tune of the first phrase (A) and sing it on the following phrases. If the harmony of the phrase is the same, the melody will fit in and, therefore, you can say that it is also an A. If it does not fit it, this means that it has a different harmony and we can say it is a B.
You can try to do the same exercise on the previous video and, in the second chorus, when there is the solo, try to sing the original melody. If you only sing the melody corresponding to the first phrase (A), you will see that it fits in the first, second and fourth phrases of the second chorus, but not in the third, since it has a different harmony and, for that reason, we call it B.
There are harmonic structures of some songs that have such good results that composers have used them to make their own pieces. Technically, in the world of jazz, this is called heads, and contrafacts in classical music (you can find more details and multiple examples in this Wiquipedia link).
One of the most commonly used harmonic structures is I Got Rhythm, by George Gershwin. It has been reused even in many later jazz styles, even composers from the Swing Era such as Count Basie (Good Bait), Duke Ellington (Cotton Tail) and Benny Goodman (Don't Be That Way) used it.
This harmonic structure is so popular that musicians call it Rhythm changes, making reference to the chords that are played on I got Rhythm. As it turns out to be so familiar, it is very common that they use it in jam sessions, to improvise.
If you like, this Spotify list will show you many more pieces with this same structure.
If you want to delve deeper into this topic you can now visit the page What sections can a song have?