NUMBER in nouns singular and plural R. A. Close 5.14 to 5.23 IR REGULAR PLURALS I N PRONUNCIATION ONLY TH from voiceless dental fricative to voiced dental fricative: BATH to BATHS MOUTH, OATH, PATH, YOUTH, BIRTH The voiceless alveolar fricative /s/ becomes voiced /z/: HOUSE to HOUSES. ending in O rule + ES: echoes, embargoes, heroes, etc. IN SPELLING ONLY E optional (both versions accepted) BUFFALO, CARGO, COMMANDO, HALO, MOSQUITO, TORNADO, VOLCANO. No E preceded by vowel or v. sound: BAMBOOS, EMBRYOS, FOLIOS, KANGAROOS, ORATORIOS, RADIOS, ZOOS. abbreviations : KILOS, MEMOS, PHOTOS musical terms of italian origin : CONCERTOS, CONTRALTOS, PIANOS, SOLOS, SOPRANOS. proper names: ESKIMOS, FILIPINOS. DYNAMOS.