Final answer:
Nonverbal cues are not necessary for a system of communication to be classified as language, which requires grammar, vocabulary, and often written symbols.
Step-by-step explanation:
The necessary criteria for classifying a form of communication as language include having a grammar (the set of rules for organizing words to convey meaning), a vocabulary or lexicon (the words of the given language), and often written symbols that represent the words or vocal sounds. However, nonverbal cues are not a necessary criterion for a system of communication to be classified as language. While nonverbal communication is symbolic and is learned through one's culture, and can accompany language, it is not a required component for a communication system to be considered a language.