In phonology, an allophone (; from the Greek , , 'other' and , , 'voice, sound') is a set of multiple possible spoken soundsor phonesor signs used to pronounce a single phoneme in a particular language. For example, in English, the voiceless plosive (as in stop ) and the aspirated form (as in top ) are allophones for the phoneme , while these two are considered to be different phonemes in some languages such as Thai. On the other hand, in Spanish, (as in dolor ) and (as in nada ) are allophones for the phoneme , while these two are considered to be different phonemes in English. The specific allophone selected in a given situation is often predictable from the phonetic context, with such allophones being called positional variants, but some allophones occur in free variation. Replacing a sound by another allophone of the same phoneme usually does not change the meaning of a word, but the result may sound non-native or even unintelligible. Native speakers of a given language perceive one phoneme in the language as a single distinctive sound and are "both unaware of and even shocked by" the allophone variations that are used to pronounce single phonemes. History of concept The term "allophone" was coined by Benjamin Lee Whorf circa 1929. In doing so, he is thought to have placed a cornerstone in consolidating early phoneme theory. The term was popularized by George L. Trager and Bernard Bloch in a 1941 paper on English phonology and went on to become part of standard usage within the American structuralist tradition. Complementary and free-variant allophones and assimilation Whenever a user's speech is vocalized for a given phoneme, it is slightly different from other utterances, even for the same speaker. That has led to some debate over how real and how universal phonemes really are (see phoneme for details). Only some of the variation is significant, by being detectable or perceivable, to speakers. There are two types of allophones, based on whether a phoneme must be pronounced using a specific allophone in a specific situation or whether the speaker has the unconscious freedom to choose the allophone that is used. If a specific allophone from a set of allophones that correspond to a phoneme must be selected in a given context, and using a different allophone for a phoneme would cause confusion or make the speaker sound non-native, the