My Definition: The "shape" of a piece of music, based on the repetition and contrast of the parts of it.
One way to think about form in music is as a plan. It tells you how the song is going to go and where there will be repetition (repeated musical moments) and contrast (noticeable differences in the music). It lays out the movement and sequence of events of a piece of music.
When it comes to analyzing or transcribing the form of a piece of music, we do that much the same way that we would for poetry: we use letters for each line. For the first line of repetition, we use "A." For all the lines of repetition that follow, we use "A" + a prime symbol like ' or '', depending on how slightly different each repetitive line is. For the contrast lines, we use "B," "C," "D," and so on. We use the same prime symbols as we do for the repetition.
Now, that was probably a bit confusing, so let's listen to an example and give it a try:
"Twinkle Twinkle Little Star" is a classic nursery rhyme that you have most likely heard and sung before. It has what we could call a simple ABA form.
Twinkle, twinkle little star, A
How I wonder what you are. A'
Up above the world so high, B
Like a diamond in the sky. B'
Twinkle, twinkle little star, A
How I wonder what you are. A'
And that's how form looks! It's really that simple. If a line sounds like the line before it, go ahead and give it the same letter. If it's clearly different, give it a new letter. And that's exactly what we just did for "Twinkle, Twinkle, Little Star." We planned out the classic nursery rhyme based on how it sounds and its repetition and contrast, which is just what form in music is.
