the Greek language created too many ambiguities when vowels went unrepresented, so the script was modified. They did not need letters for the guttural sounds represented by aleph, he, heth or ayin, so these symbols were assigned vocalic values. The letters waw and yod were also adapted into vowel signs; along with he, these were already used as matres lectionis in Phoenician. The major innovation of Greek was to dedicate these symbols exclusively and unambiguously to vowel sounds that could be combined arbitrarily with consonants (as opposed to syllabaries such as Linear B which usually have vowel symbols but cannot combine them with consonants to form arbitrary syllables). Abugidas developed along a slightly different route. The basic consonantal symbol was considered to have an inherent "a" vowel sound. Hooks or short lines attached to various parts of the basic letter modify the vowel. In this way, the South Arabian abjad evolved into the Ge'ez abugida of Ethiopia between the 5th century BC and the 5th century AD. Similarly, the Brāhmī abugida of the Indian subcontinent developed around the 3rd century BC (from the Aramaic abjad, it has been hypothesized). The other major family of abugidas, Canadian Aboriginal syllabics, was initially developed in the 1840s by missionary and linguist James Evans for the Cree and Ojibwe languages. Evans used features of Devanagari script and Pitman shorthand to create his initial abugida. Later in the 19th century, other missionaries adapted Evans's system to other Canadian aboriginal languages. Canadian syllabics differ from other abugidas in that the vowel is indicated by rotation of the consonantal symbol, with each vowel having a consistent orientation. Abjads and the structure of Semitic languages The abjad form of writing is well-adapted to the morphological structure of the Semitic languages it was developed to write. This is because words in Semitic languages are formed from a root consisting of (usually) three consonants, the vowels being used to indicate inflectional or derived forms. For instance, according to Classical Arabic and Modern Standard Arabic, from the Arabic root Dh-B-Ḥ (to slaughter) can be derived the forms (he slaughtered), (you (masculine singular) slaughtered), (he slaughters), and (slaughterhouse). In most cases, the absence of full glyphs for vowels makes the common root clearer, allowing readers to guess the meaning of unfamiliar words from familiar roots (especially in conjunction with context clues) and improving word recognition while reading for practiced readers. By contrast,