Probably the most important skill for a musician is understanding what a composer is trying to say in his or her music. To do this, you should visualize how the music develops the idea as it proceeds and where each sentence starts and ends. For example, a musician understanding the cadences might be able to see the basic structure. Otherwise, it is like a baby who hears the sound but does not understand. Let us experience how a musician actually uses the form when composing to state the musical idea properly.
Let us think about what the form means in music. A good structure gives a framework in which musical ideas relate logically. Musical creativity starts with a simple musical idea (often called a motive), but the true beauty comes when the composer determines its potential and develops the piece without losing or dulling that idea. We don’t call a piece “musical” if ideas are presented one after another without a relationship between them or when an idea is repeated over and over without change. Music is a statement written by a composer. To deliver the message, the piece must not only carry through the idea, but also consistently develop and transform it as other ideas are introduced.
The form is a very basic tool that a composer utilizes to develop the idea properly. Not every composer considers form when writing, but a lot of known musical forms – sonata, fugue, song form, variations, etc. – can offer a minimum security to a piece to keep originality. (And, the conventional forms often inspire composers when constructing the music.) These forms are well-established and still used widely because they help musical ideas unfold logically and convince listeners as well.