'passive'. Christopher Ehret has proposed that Proto-Afroasiatic originally had as many as thirty-seven separate verbal extensions, many of which then became fossilized as third consonants. This theory has been criticized by some, such as Andrzej Zaborski and Alan Kaye, as being too many extensions to be realistic, though Zygmont Frajzyngier and Erin Shay note that some Chadic languages have as many as twelve extensions. "Prefix conjugation" Conjugation of verbs using prefixes that mark person, number, and gender can be found in Semitic, Berber, and in Cushitic, where it is only found on a small set of frequent verbs. These prefixes are clearly cognate across the branches, although their use within the verbal systems of the individual languages varies. There is a general pattern in which n- is used for the first person plural, whereas t- is used for all forms of the second person regardless of plurality or gender, as well as feminine singular. Prefixes of ʔ- (glottal stop) for the first person singular and y- for the third person masculine can also be reconstructed. As there is no evidence for the "prefix conjugation" in Omotic, Chadic, or Egyptian, it is unclear whether this was a Proto-Afroasiatic feature that has been lost in those branches or is a shared innovation among Semitic, Berber, and Cushitic. "Suffix conjugation" Some AA branches have what is called a "suffix conjugation", formed by using pronominal suffixes to indicate person, gender, and number and a verbal adjective. In Akkadian, Egyptian, Berber, and Cushitic this forms a "stative conjugation", used to express the state or result of an action; the same endings as in Akkadian and Egyptian are also present in the West Semitic perfective verb form. In Akkadian and Egyptian, the suffixes appear to be reduced forms of the independent pronouns (see Pronouns); the obvious correspondence between the endings in the two branches has been argued to show that Egyptian and Semitic are closely related. While some scholars posit an AA origin for this form, it is possible that the Berber and Cushitic forms are independent developments, as they show significant differences from the Egyptian and Semitic forms. The Cushitic forms in particular may be derived from morphology found in subordinate clauses. "Nisba" derivation The so-called "Nisba" is a suffix used to derive adjectives from nouns and, in Egyptian, also from prepositions. It is found in Egyptian, Semitic, and possibly, in some relic forms, Berber.