In the past, songs from the 1960s and 1970s were even shorter, only 2 and a half to 3 minutes. This is because the length of each section of a general song is between 16 and 32 bars, and then there is the chorus of 16 bars, and then the general song is about 3-4 sections, which adds up to about 3 minutes. At that time, there was an English song "American Pie", which had four sections of 64 measures, and the total length was more than 8 minutes.

The current songs are 4-5 minutes long, which means the way of composing music has been changed. In the past, when adding a chorus to three verses, you would usually sing two verses first, then come back and sing the third verse before ending, which is A A B A style. Modern songs are often A B A B C A B, that is, every verse A is followed by chorus B. After 2 verses, sing another introduction C (the introduction of this C may be very short, only 8 bars, that is, two sentences), and when you come back, sing the last verse plus the chorus.

The above is the basic structure of general composition. All composers follow these formats. This is formed based on people's general habits. There is no regulation by anyone. It's just that if you don't know whether the audience will accept your song, how dare you use the resources of 2 songs to make 1 song!

Supplement:

After a long time, people who sing will be tired and people who listen will be annoyed