Nouns and adjectives are divided into three groups depending on the last consonant of their stems. Stem is the part of a word that remains after removing its ending:
bratr brother stem: bratr-
sotra sister stem: sotr-
mloko milk stem: mlok-
nowy new stem: now-
słódki sweet stem: słódk-
When declining a noun or an adjective it is essential to know to which group it belongs in order to choose the right declension pattern and case endings.
If the last consonant of a stem is b, c, d, ł, m, n, p, r, s, t, w or z the stem is called a hard stem. Stems ending in c, s and z form a subgroup called hard hissing stems.
Some hard-non-hissing-stem nouns and adjectives:
zrudoba sadness stem: zrudob-
moda fashion stem: mod-
koło wheel stem: koł-
kał cabbage stem: kał-
skłon slope stem: skłon-
chory ill stem: chor-
Some hard-hissing-stem nouns and adjectives:
połojca half stem: połojc-
wokrjes district stem: wokrjes-
lózy impertinent stem: lóz-
Stems ending in h, ch or k are called velar stems.
Some velar-stem nouns and adjectives:
dróha road stem: dróh-
pjatk Friday stem: pjatk-
hłuchi deaf stem: hłuch-
Stems ending in bj, č, ć, dź, ń/nj, j, l, pj, rj, š, wj or ž are soft stems.
Some soft-stem nouns and adjectives:
polo field stem: pol-
njebjo sky stem: njebj-
třeći third stem: třeć-
Assigning masculine nouns to stem groups is a bit more complicated as the basic forms of masculine nouns given in dictionary entries (Nom.sing.) usually end in a zero ending. This means that their basic forms consist of a bare stem not followed by any vowel. As the distinction between some hard and soft consonants is lost in this position (when not followed by a vowel), the hardness or softness of a stem may, in some cases, not be visible in the basic forms.
This applies to the masculine nouns ending in the the labial consonants b, m, p, w, or in r. In order to determine whether their stem is hard or soft we need to know any other of their case forms, other than the basic Nom.sing. form.
Both dub oak and hołb pigeon end in -b but they behave differently when a non-zero ening is added to their stems:
As we can see, the last consonant of dub remains unchanged (hard) in the Gen.sing. but in hołb it changes to a soft bj. Thus, dub (stem: dub-) is a hard-stem noun and hołb (hołbj-) is a soft-stem noun.
All other masculine nouns not ending in b, m, p, w or r folow the general rule.
As is the case with masculine nouns, the hardness or softness of some adjectives may not be visible from the way the last consonant of their stems is written in the basic form (Nom.sing.masc.). Both rjany beautiful and tuni cheap have their last consonants written -n-. The difference between them arises from the fact that the ending vowel y doesn’t effect the preceeding consonant, whereas any consonant followed by an i is always automatically softened in pronunciation. Thus the stem of rjany is rjan- but the stem of tuni is in fact tunj- with a soft nj at the end. The difference between these two adjectives becomes evident if we compare their case forms that are made using an ending beginning with any other vowel than y and i:
All the adjectives with the basic form ending in -y are hard-stem no matter what their last consonant is (as y may only follow hard consonants in Upper Sorbian).
However, not all the adjectives ending in -i are soft-stem. Namely, adjectives ending in -hi, -chi or -ki are velar-stem.
drohi expensive stem: droh-
hłuboki deep stem: hłubok-
All the other adjectives ending in -i are soft-stem.
lětni reffering to summer stem: lětnj-
srěni average stem: srěnj-