Nonverbal communication describes the processes of conveying a type of information in a form of non-linguistic representations. Examples of nonverbal communication include haptic communication, chronemic communication, gestures, body language, facial expressions, eye contact etc. Nonverbal communication also relates to the intent of a message. Examples of intent are voluntary, intentional movements like shaking a hand or winking, as well as involuntary, such as sweating. Speech also contains nonverbal elements known as paralanguage, e.g. rhythm, intonation, tempo, and stress. It affects communication most at the subconscious level and establishes trust. Likewise, written texts include nonverbal elements such as handwriting style, the spatial arrangement of words and the use of emoticons to convey emotion.
Nonverbal communication demonstrates one of Paul Watzlawick's laws: you cannot not communicate. Once proximity has formed awareness, living creatures begin interpreting any signals received. Some of the functions of nonverbal communication in humans are to complement and illustrate, to reinforce and emphasize, to replace and substitute, to control and regulate, and to contradict the denotative message.
Nonverbal cues are heavily relied on to express communication and to interpret others' communication and can replace or substitute verbal messages. However, non-verbal communication is ambiguous. When verbal messages contradict non-verbal messages, observation of non-verbal behaviour is relied on to judge another's attitudes and feelings, rather than assuming the truth of the verbal message alone.
There are several reasons as to why non-verbal communication plays a vital role in communication:
"Non-verbal communication is omnipresent."  They are included in every single communication act. To have total communication, all non-verbal channels such as the body, face, voice, appearance, touch, distance, timing, and other environmental forces must be engaged during face-to-face interaction. Written communication can also have non-verbal attributes. E-mails and web chats have options to change text font colours, stationary, emoticons, and capitalization in order to capture non-verbal cues into a verbal medium.
"Non-verbal behaviours are multifunctional."  Many different non-verbal channels are engaged at the same time in communication acts and allow the chance for simultaneous messages to be sent and received.
"Non-verbal behaviours may form a universal language system."  Smiling, crying, pointing, caressing, and glaring are non-verbal behaviours that are used and understood by people regardless of nationality. Such non-verbal signals allow the most basic form of communication when verbal communication is not effective due to language barriers.