Most songs written in popular music follow song forms. Song forms are structures containing various sections that may or may not be repeated within the song. Though there are a number of traditional song forms that are used commony, a song form may also be derived from existing ones to suit the need. 

Some of the most common song forms may include the strophic form (AAA), the 12-bar blues form (AAB), the 32-bar form (AABA) and so on. It is very important for any songwriter to have knowledge of the various song forms and its application in order to write more sensibly and to express themselves better.

Pat Pattinson, a professor at Berklee College of Music once said "There are no rules to songwriting, only tools". Aptly, the following article gives you an overview to be able to use its knowledge where needed.

http://www.songstuff.com/song-writing/article/song-form-overview/

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