The following is an overview of the grammar of the Slovene language.
As in most other Slavic languages, changes to consonants and vowels often occur between related forms of words. Most of these can be traced back to changes that occurred in the ancestral Proto-Slavic language. Over time, many of the original changes have been reversed or levelled out.
The following table gives an overview of the above changes:
These changes are very similar to those found in the related Serbo-Croatian language, but in iotation, Slovene j corresponding to Serbo-Croatian đ, and č with ć.
Word stems that end in c, č, š, ž or j are called "soft" stems, while the remainder is "hard". When endings begin with -o-, this vowel usually becomes -e- after a soft stem; this is called "preglas" in Slovene. This happens in many noun and adjective declensions, and also in some verbs. For example, the instrumental singular form of korak "step" is korakom, while for stric "uncle" it is stricem.
There are also some instances where the vowel stays as o, such as the accusative singular of feminine nouns. These instances can be traced back to an earlier nasal vowel ǫ in Proto-Slavic, which did not undergo this change.
When certain hard-to-pronounce consonant clusters occur word-finally, an additional fill vowel is inserted before the last consonant(s) of the word to break up the cluster. This typically happens where there is no ending, like in the nominative singular, or the genitive dual and plural. The fill vowel is usually a schwa (/ə/, spelled e). For example, the noun igra "game" has the genitive plural form iger, not igr.
If the last consonant is j, then i is used as the fill vowel instead. For example, ladja "boat" has the genitive plural ladij. However, if the stem ends in lj, nj or rj, then the fill vowel is the normal e and is inserted before both consonants. The noun ogenj "fire", for example, loses the fill vowel in the genitive singular form ognja.
There are a few cases where the fill vowel is instead a stressed a. These are irregular and must simply be memorized. An example is ovca "sheep", which is ovac in the genitive plural, not ovec.