Class of declension in Nûrlâm affects the form of cases and in other dialects also plural number. This term is applicable mainly to nouns and pronouns but also to adjectives and even case postpositions. There are only two classes for all lexical categories:

 I. words ending with consonants 
II. words ending with vowels or diphtongs

However as Black Speech has tendency to join short words together as clitics, declension class is not fixed for one word stem. In example “uruk” (orc) belongs to declension class I, but adding clitic adjective “kû” (old) to it changes the declension class of resulting word “uruk(k)û” (old orc) to class II. Adding derivational suffixes (like feminizer suffix -niz) also may change declension class. The most of grammatical forms are the same for both declension classes but difference appears when adding suffix or clitic starting with vowel (including dialectical plural markers -i, -u, -û). Plural marker is replaced with -z for declension class II. The same suffix -z- is inserted between roots ending with vowel and case suffixes starting with vowel. However there are some exceptions (see article about cases) specially for pronouns. If both case suffix and plural marker are required then case clitic postposition is added first according to root's declension class and plural suffix according to declension class of this clitic. Examples:

1. Noun's suffix chain in Nûrlâm
2. Wikipedia article about declension