The quick-and-simple definition of phonology is, "the study of sound patterns in human language."

Fine, you say, but what exactly is a "sound pattern"? Here are some examples:

• segments (consonants and vowels) -- How many consonants and vowels are used by a given language? What is the set of sound properties (features) needed to classify those segments?

• tones -- Does a given language use tones to distinguish among words? If so, how many distinct tones are used? How should different tones be classified?

• larger units -- How does a given language allow segments to combine in forming larger units like syllables and words? How are tones associated with syllables or words?

• alternations -- Why do certain sounds change their properties when they occur in particular environments (i.e., near other sounds of a certain type, at word or syllable edges, etc.)?
  • An example from English: The pluralizer, spelled (e)s, is pronounced differently in the word dogs from the way it is pronounced in cats? How can the difference in pronunciation between the two alternants of the pluralizer be characterized? What factor makes the pronunciation of the pluralizer alternate?

Phonologists are interested in answering questions like these for individual languages, but they are also interested in comparing languages to see where similarities and differences emerge.

An ideal theory of the human phonological system is general, but restrictive. Every normally developing human infant has the potential to acquire whatever human language it is exposed to, so our phonological theory should be general and flexible enough to encompass all the naturally occurring phonological phenomena that we encounter. At the same time, we would like our theory to be restrictive enough not to generate any phonological patterns that are impossible in human language.

Balancing these two goals is difficult, but the tension between generality and restrictiveness often leads to new understanding of how sounds pattern in human language.

Of course, not all human languages use speech sounds. Manual (signed) languages use handshapes, hand positions, and ... [finish this -- find good link with overview]