This is a period - the smallest musical form which has only one complete musical idea. Let's break this sentence into several segments and you'll see what I mean with this definition.
The period can be a complete musical composition or it can be a part of a longer piece. The length of the period can be anywhere from 4 to 64 measures. The most commonly found periods are 8-16 measures long.
The period has to have only one musical idea and it has to be complete. For example, if there are several contrasting musical fragments in the piece, chances are that the form of such piece is more complex than a period.
Also the musical idea has to be complete. For example, if you hear a fragment of the piece after which follows it's repetition (exact or with a different ending) - it's not two periods but only one (because the musical idea is the same in this case).
Now take your organ piece which you are working on right now and try to identify the first period in it. Post your answer in the comments bellow. Write in the composer's name, title of the piece and measure numbers of the first period.
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