The difficulty of the transliteration is greatly enhanced by the fact that the same sign represents both _m_ and _w_, and the three gradations of sound—the surd, aspirate and sonant—are not distinguished by separate signs. It is therefore impossible to say in many cases whether to transcribe _m_ or _w_, _k_ or _g_, _p_ or _b_, _f_ or _d_; and Oppert has enumerated no less than six different modifications of sounds—_č_ (_tch_), _ḡ_ (_dj_), _z̆_, _ts_, _dz_, and _z_—that are all represented by a single sign.[688] Weisbach points out that _g_, is only clearly distinguished from _k_ when it occurs before _i_. The Median _z_ represents the Persian _z_, _c_, _j_, and the Babylonian _s_ (and _o_?); the _r_ and _n_ are sometimes found to be interchangeable. When the sound cannot be checked by its occurrence in a proper name, Oppert generally adopts the hard sound; but he allows himself a certain latitude in the application of this rule, and he shows a decisive preference of _w_ to _m_. Weisbach follows the uniform practice of transcribing the gutturals, dentals and labials by the tenues; he always uses _z_ for the Persian _c_, _j_ and _z_, and for the Babylonian _z_ and _s_; and, contrary to Oppert, he prefers _m_ to _w_. Oppert recognises the five vowels _a_, _e_, _i_, _o_ and _u_; and, following De Saulcy, he admits _yi_, _ya_ and _ah_ in his list, among vowels. Weisbach excludes the _o_, for he considers there was no difference of sound between it and _u_; the _y_ he includes among the semi-vowels, with both _r_ and _l_. Although Oppert found that all the five vowels follow the consonant to form the single syllable, he considered that only _a_, _i_ and _u_ precede it. Both writers agree to limit the consonantal sounds to about eleven. Oppert was the first to treat the grammar with elaborate care, and when he claimed that his work was ‘une création entièrement nouvelle,’ the statement was probably more strictly accurate than he imagined. The nouns do not admit of any distinction of gender, and have only the singular and plural number. Oppert distinguishes no fewer than twelve different cases, indicated by suffixes, a profusion limited by Weisbach to eight, viz. nominative, genitive, accusative, dative, ablative, allative, locative and comitative.