In order to be able to capture information about the specific sounds made when people speak (in any language), we have systems of classification. Humans are capable of making a large variety of different speech sounds, and the IPA chart describes all of the sounds that researchers have found to be used in human speech. It is organised based on the different ways that sounds are articulated.

Information relevant to articulation which the chart describes includes:

• Place of articulation. This includes, e.g. "bilabial" - both lips, "labiodental" - lips and teeth, etc..
• Manner of articulation. For example "trill", "fricative"
• whether the sound is voiced or voiceless
• (for vowels) the position of the tongue inside the mouth
  • The proximity of the tongue to the palate is described using close, close-mid, open-mid and open
  • which part of the tongue is raised - front, central or back
  • whether the mouth is rounded or spread

The symbols on the IPA chart are phonetic symbols. For any given language, only a subset of these sounds will be linguistically significant - some of them may not be used at all; in other cases it could be that a given utterance would not have its meaning changed by changing the phonetic symbol used to transcribe it.

When transcribing speech of a certain language, the symbols written are phonemic symbols, or phonemes. In most cases, the phonemes for English have the same sound as the equivalent phonetic symbols, but not always (e.g. "r"). Phonetic transcriptions are conventionally written with square bracket delimiters; phonemic are bracketed by forward slashes. Thus the phonetic and phonemic transcriptions of "ostrich" in RP English are:

An allophone "is one of several similar speech sounds belonging to a phoneme. Each allophone is the form of the phoneme used in a specific context." (Wikipedia). So for example, the following two phonetic symbols represent allophones of the RP phoneme /r/:

Useful book readings for this lecture:

• Roach: "Phonetics", ch. 3
• Fromkin: "An Introduction to Language", ch. 7
• Crystal: "Encyclopedia of Language", ch. 28