occurs in Hebrew in a few nouns (šana means "one year", šnatayim means "two years", and šanim means "years"), but for those it is obligatory. The curious phenomenon of broken plurals – e.g. in Arabic, sadd "one dam" vs. sudūd "dams" found most profusely in the languages of Arabia and Ethiopia, may be partly of proto-Semitic origin, and partly elaborated from simpler origins. Verb aspect and tense All Semitic languages show two quite distinct styles of morphology used for conjugating verbs. Suffix conjugations take suffixes indicating the person, number and gender of the subject, which bear some resemblance to the pronominal suffixes used to indicate direct objects on verbs ("I saw him") and possession on nouns ("his dog"). So-called prefix conjugations actually takes both prefixes and suffixes, with the prefixes primarily indicating person (and sometimes number or gender), while the suffixes (which are completely different from those used in the suffix conjugation) indicate number and gender whenever the prefix does not mark this. The prefix conjugation is noted for a particular pattern of prefixes where (1) a t- prefix is used in the singular to mark the second person and third-person feminine, while a y- prefix marks the third-person masculine; and (2) identical words are used for second-person masculine and third-person feminine singular. The prefix conjugation is extremely old, with clear analogues in nearly all the families of Afroasiatic languages (i.e. at least 10,000 years old). The table on the right shows examples of the prefix and suffix conjugations in Classical Arabic, which has forms that are close to Proto-Semitic. In Proto-Semitic, as still largely reflected in East Semitic, prefix conjugations are used both for the past and the non-past, with different vocalizations. Cf. Akkadian niprus "we decided" (preterite), niptaras "we have decided" (perfect), niparras "we decide" (non-past or imperfect), vs. suffix-conjugated parsānu "we are/were/will be deciding" (stative). Some of these features, e.g. gemination indicating the non-past/imperfect, are generally attributed to Afroasiatic. Proto-Semitic had an additional form, the jussive, which was distinguished from the preterite only by the position of stress: the jussive had final stress while the preterite had non-final (retracted) stress. The West Semitic languages significantly reshaped the system. The most substantial changes occurred in the Central Semitic languages (the ancestors of modern Hebrew, Arabic and Aramaic). Essentially, the old prefix-conjugated jussive or preterite became a new non-past (or imperfect), while the stative became a new past (or