Speech is the vocalized form of communication used by humans and some animals, which is based upon the syntactic combination of items drawn from a finite set of categories. It is usually the primary means by which people communicate, although visual methods such as body language and sign language may also be used. Speech differs from written language in that it involves continuous sound waves produced by the vocal cords, whereas written language uses symbols such as letters that are combined into words to create sentences. The production of speech also requires motor control of the lips, tongue, and other articulators.
The term “speech” can also refer to the actual content of what is being communicated, as well as the act of communicating itself. For example, one might say “I gave a speech on global warming”, or “She made a speech about her experiences in Africa”. In many cases, what someone says during a speech may be more important than how they say it; however, delivery (including facial expressions and gestures) can also play an important role in conveying meaning.
Humans have developed various ways of producing speech sounds (or phonemes), including using their teeth, tongues, lips and lungs. The airstream mechanism used to produce speech sounds varies depending on the languages spoken; for example, English speakers use pulmonic egressive airstream while speaking, while many Native American languages use glottalic ingressive airstream. The type of airstream mechanism used does not affect the meaning of what is being said; however, it can affect how easily sounds are distinguished from each other (e.g., whether two different vowel sounds are pronounced identically).
The study of speech production is known as phonetics; this field includes both production-oriented work (e.g., investigating how different sounds are produced) and perception-oriented work (e.g., investigating how listeners identify particular sounds). Phonetics is closely related to linguistics—the scientific study of language—since understanding how speech is produced can provide insights into how languages are structured. Linguists working within generative grammar propose that there is a universal underlying structure to all human languages; this hypothesis has implications for our understanding of both how children acquire language and how adults produce it..