Sometimes I'H start a sentence in Spanish Y TERMINOEl\fESPANOl: toward a typologyo·f code-switching 1 SHANA POPLACK J. Abstract , The occurr.ence of co.de-switching, or the, ser:mzngly random alternation of two languages both between and within sentences; has been shown (Gumperz; 1976;· Pfciff,.1975; Well'tZ, i977) to' be· governed not only by, extra'-lingufstic but also linguistic!actors. For the balanced bilingual,(}'Ode- switching appears to be subject to an 'equivalence ciJnstraint' (Poplack, 1978): i:e. irtends to occur cit points in discourse wherejuxtaposiiion of L 1 and L 2 elements does not violate a rule of eithe.r !If cbrreci;ilie equivalence constraint ·on c@de'l'switchingmay to measure 'degrr;e of bilingy,al 'ability./ It was Hypothesized that.·equivalence are 'risky' in .terms of syntactic well-formedness (i.e. those· which occUr .withih a sentencf) would tend to be avoidedaltogether. To test this hyp'oth- esis; 1 analysed the speech of 20 Puerto Rican residents of a stable bilingual . . community, exhibiting varying degrees of bilingual ability: Quantitative . analysis of'their switches fevealed that bothfluent andnon-fluentbilinguals .. were able to code-switchfrequently and still maintain grammaticality in both L i 'and L 2 ,. While fluent bilinguals tended to switch at vtirious syntactic boundaries within the sentence, non-fluent bilinguals favoured switching / . . between sentences, allowing them to participate in the code-switching mode, without fear of violating a grammatical rule' of either of the, languages' involved.. These rr,esults suggest that. the code-switching mode proceeds from thtU area of the bilingual's grammar where the surface structures of t 1 ' and L 2 overlap, and that code-switching, ratker than representing debasement of linguistic skill, is actually a sensitive indicator of bilingual ability. . . Linguistics 18 (1980), 581-618. 0024/3949/80/0018-0581 $2.00 © Mouton Publishers, The Hague