There are two groups of nominals with a basic form ending in a short
vowel+s. The most common of these is the type ajatus ‘thought’ (cf.
§20.3).
§20.3 TAIVAS NOMINALS
In nominals like taivas ‘heaven’ the -s of the basic form alternates with a
vowel identical with the preceding vowel.
In ajatus nominals -s changes to -kse- in the inflectional stem; the
partitive singular is formed directly from the basic form
