Paralanguage refers to the non-verbal elements of communication used to modify meaning and convey emotion. Paralanguage may be expressed consciously or unconsciously, and it includes the pitch, volume, and, in some cases, intonation of speech. Sometimes the definition is restricted to vocally-produced sounds. The study is known as paralinguistics.
The term 'paralanguage' is sometimes used as a cover term for body language, which is not necessarily tied to speech, and paralinguistic phenomena in speech. The latter are phenomena that can be observed in speech (Saussure's parole) but that do not belong to the arbitrary conventional code of language (Saussure's langue).
The paralinguistic properties of speech play an important role in human speech communication. There are no utterances or speech signals that lack paralinguistic properties, since speech requires the presence of a voice that can be modulated. This voice must have some properties, and all the properties of a voice as such are paralinguistic. However, the distinction linguistic vs. paralinguistic applies not only to speech but to writing and sign language as well, and it is not bound to any sensory modality. Even vocal language has some paralinguistic as well as linguistic properties that can be seen (lip reading, McGurk effect), and even felt, e.g. by the Tadoma method.
One can distinguish the following aspects of speech signals and perceived utterances:
Some of the linguistic features of speech, in particular of its prosody, are paralinguistic or pre-linguistic in origin. A most fundamental and widespread phenomenon of this kind is known as the "frequency code" (Ohala, 1984). This code works even in communication across species. It has its origin in the fact that the acoustic frequencies in the voice of small vocalizers are high while they are low in the voice of large vocalizers. This gives rise to secondary meanings such as 'harmless', 'submissive', 'unassertive', which are naturally associated with smallness, while meanings such as 'dangerous', 'dominant', and 'assertive' are associated with largeness. In most languages, the frequency code also serves the purpose of distinguishing questions from statements. It is universally reflected in expressive variation, and it is reasonable to assume that it has phylogenetically given rise to the sexual dimorphism that lies behind the large difference in pitch between average female and male adults.
In text-only communication such as email, chatrooms and instant messaging, paralinguistic elements can be displayed by emoticons, font and color choices, capitalization and the use of non-alphabetic or abstract characters. Nonetheless, paralanguage in written communication is limited in comparison with face-to-face conversation, sometimes leading to misunderstandings.