The alternation of stem-internal а and о: Can we say that it is determined by pragmatics?

This article critically examines the hypothesis regarding the emergence of the sound [o] in the place of the expected [a] (and, accordingly, in written form, the occurrence of о in the place of the expected а) is a regular mechanism marking the informality of a word (its association with slang, colloquial language, and other non-standardized areas of the language). It shows that externally similar phenomena conceal completely different linguistic mechanisms. In particular, quite often the appearance of о is a side effect of the shifted stress in word inflection. The examples considered confirm a general principle of spell checking: slang and colloquial words cannot be used for checking. It is claimed that this principle should be taken into account in spelling guides and references.