Phonetic transcription (also known as phonetic script or phonetic notation) is the visual representation of speech sounds (or phones) by means of symbols. The most common type of phonetic transcription uses a phonetic alphabet, such as the International Phonetic Alphabet. Versus orthography The pronunciation of words in all languages changes over time. However, their written forms (orthography) are often not modified to take account of such changes, and do not accurately represent the pronunciation. Words borrowed from other languages may retain the spelling from the original language, which may have a different system of correspondences between written symbols and speech sounds. Pronunciation can also vary greatly among dialects of a language. Standard orthography in some languages, such as English and Tibetan, is often irregular and makes it difficult to predict pronunciation from spelling. For example, the words bough, chough, cough, though and through do not rhyme in English even though their spellings might suggest otherwise. Other languages, such as Spanish and Italian have a more consistent (but still imperfect) relationship between orthography and pronunciation, while a few languages may claim to have a fully phonemic spelling system (a phonemic orthography). For most languages, phonetic transcription makes it possible to show pronunciation with something much nearer to a one-to-one relationship between sound and symbol than is possible with the language's orthography. Phonetic transcription allows one to step outside orthography, examine differences in pronunciation between dialects within a given language and identify changes in pronunciation that may take place over time. A basic principle of phonetic transcription is that it should be applicable to all languages, and its symbols should denote the same phonetic properties whatever the language being transcribed. It follows that a transcription devised for one individual language or group of languages is not a phonetic transcription but an orthography. Narrow versus broad transcription Phonetic transcription may be used to transcribe the phones of a language. In all systems of transcription there is a distinction between broad transcription and narrow transcription. Broad transcription indicates only the most noticeable phonetic features of an utterance, whereas narrow transcription encodes more information about the phonetic characteristics of the allophones in the utterance. The difference between broad and narrow is a continuum, but the difference between phonemic and phonetic transcription is usually treated as a binary distinction. Phonemic transcription is a particular form of broad transcription which disregards all allophonic difference; as the name