There are two parts to Form: message mode and syntax.
Mode: Messages can be transmitted many different ways and include symbol systems (sign language, picture representations, icons, writing or speech) gestures, body language, and even behavior.
Syntax: Form includes grammar, word order, word endings, verb tenses, and more. It is the ability to put concepts together for different meaning for example:
The form can be transmitted with any symbol system (sign language, picture representations, icons, writing or speech). Another example of syntax is combining a word (dog) and then changing the meaning by adding another word (barking dog, big dog, friendly dog).This is an area often neglected when teaching AAC.