The terms speech and language are related, but refer to different aspects of the communication process. We'll begin our discussion by considering the term 'language' first. Language has been defined by Crystal (1987) as: The systematic, conventional use of sounds, signs, or written symbols in a human society for communication and self-expression (p. 424).
Language is a complex, often arbitrary, rule-governed system. It is complex in that we can identify subsystems of language (see below). It is often arbitrary in that words and language rules are likely to differ from one language community (such as American English) to another (such as French). In other words, there is nothing about four legged animals who bark that makes us use the word dog to describe them; we could use the word chien just as easily. Finally, language is rule-governed in that speakers of a language agree that some constructions are permitted (for example, John likes to read books), whereas other constructions are prohibited as ungrammatical (for example, Read John books to likes).
Linguists (scientists who seek to describe and explain language) often differentiate among five subsystems of language:
Pragmatics: Rules
that govern language use.
Pragmatic abilities include language function (for example, what do we
hope to achieve through communication), directness (give me some pie is
more direct than that pie looks good), appropriateness, as well
as interpersonal factors such as assumptions regarding shared
knowledge, knowing when to introduce or change topics, etc.
Semantics: Rules
that govern language content.
The Semantic subsystem is concerned with the meaning of words
(vocabulary) as well as the role that words play in communication. For
example, consider the following sentences:
Pat hugged the doll.
The doll was hugged by Pat.
In both sentences, Pat was the "hugger" (the agent) and the doll
was the "huggee" (the object receiving the force of the action 'hug').
Syntax: Rules that
govern formulation of grammatical sentences, especially ordering of
words.
Syntactic rules dictate the structure of phrases and how those phrases
are combined into sentences. In addition, syntax allows us to rearrange
words to make new sentences. For example, the words in the declarative
sentence It is raining. can be rearranged to ask the
question, Is it raining?
Morphology: Rules
associated with the formation of words.
Words can be broken down into smaller units called morphemes. The word cats,
for example, is made of two morphemes: cat meaning feline
and -s meaning more than one. Morphology and syntax comprise
what many of us think of as grammar.
Phonology: Rules
associated with the sound system of a language.
The rules of phonology determine what sounds are used by a speaker of a
language, when they are used, and how they can be combined. Also,
phonological rules describe sound changes. For example, we pronounce
the word electric with a [k] sound at the end. If we add
the suffix -ity to form electricity, then the
pronunciation changes and the [k] sound is lost and an [s] is
pronounced instead.
From this description, we
can see that language is a complex, abstract concept. Language
can be written, spoken, or signed (as in American Sign Language). The
spoken form of language is speech. Speech parameters
include production of voice, movement of the oral structures to produce
speech sounds (articulation), and smoothness of speech production
(fluency).