Functional load

In linguistics and especially phonology, functional load refers to the importance of certain features in making distinctions in a language. English vowels, for example, have a very high functional load: There are innumerable sets of words distinguished (see minimal pair) just by their vowels, such as "pin, pen, pan, pun, pain, pine". Voicing is similar, as can be seen in "pat - bad, sue - zoo". Speakers who do not control these differences will be very difficult to understand.

However, although voicing is generally important in English, the voicing difference between the two fricatives written "th", IPA| [θ, ð] , has a very low functional load: It is difficult to find meaningful distinctions dependent solely on this difference. One of the few examples is "thigh" vs. "thy" although they can be distinguished from context alone. Similar is the difference of "j" IPA| [dʒ] vs. "zh" IPA| [ʒ] , as in "virgin" vs. "version". The difference between the two "ng" sounds, IPA| [ŋ, ŋg] , found in "singer" and "finger", is so unimportant that it makes no practical difference if one mixes them up. The functional load is nearly zero.

The term "functional load" goes back to the days of the Prague School; references to it can be found in the work of Vilem Mathesius in 1929. Its most vocal advocate was André Martinet, a historical linguist who claimed it was a factor in the likelihood of a phonological mergerref|Martinet. He predicted that perceptually similar pairs of phonemes with low functional load would merge. This has not been proved empirically; indeed, all empirical tests have come out against it.

There is no standard measurement for Functional Load. A popular measure is the number of minimal pairs, but this does not take into account word frequency and is difficult to generalize beyond binary phonemic oppositions. Charles Hockett proposed an information theoretic definition in 1955ref|Hockett, which has since been generalized. Now, given a large text corpus, one can compute the Functional Load of any phonological contrast including distinctive features, suprasegmentals, and distinctions between groups of phonemes. For instance, the Functional Load of tone in Putonghua (Mandarin Chinese) is as high as that of vowels; meaning that the loss of information when all tones sound alike in Putonghua is approximately equal to that when all vowels sound alike in the language.

References

Économie des changements phonétiques: Traité de phonologie diachronique. Par ANDRÉ MARTINET. (Bibliotheca romanica, Series prima: Manualia et cornrnentationes, No. 10.) Pp. 396. Berne: editions A. Francke S. A., 1955

A manual of phonology. By CHARLES F. HOCKETT("International journal of American linguistics", Vol. 21, No. 4, Part 1 [October 19551 = Indiana University publications in anthropology and linguistics, Memoir 11 of IJAL.) Pp. v, 246. Baltimore: Waverly Press (for Indiana University, under the auspices of [the] Linguistic Society of America [and the] American Anthropological Association), 1955.