The quality of consonants (palatalised or non-palatalised) is indicated in writing by the vowels surrounding them. So-called "slender" consonants are palatalised while "broad" consonants are neutral or velarised. The vowels and are classified as slender, and , , and as broad. The spelling rule known as ("slender to slender and broad to broad") requires that a word-medial consonant or consonant group followed by a written or be also preceded by an or ; and similarly if followed by , or be also preceded by an , , or .