The article describes the linguistic behavior of the introductory phrase stalo byt’ (literally became to be, meaning roughly ‘so’) in the Russian language of the XVIII - XXI centuries. The data from the Russian National Corpus show that this construction acquired additional senses over the centuries. Firstly it was used as a reason and cause marker, then it also developed two discourse meanings: paraphrase and returning to a previous theme. Our data show that this development is correlated with the increasing use of stalo byt’ in dialogues. In the Russian language of the XVIII – XIX centuries there was a variant of stalo byt’ – a single introductory word stalo (literally became), the difference between the constructions being rather stylistic than grammatical. Stalo while being the most preferable and prestigious in the language of the XVIII century, by the beginning of the XIX century became to sound archaic and thus vernacular. Finally, by the end of the XIX century parenthetical stalo almost disappeared. We suppose that this kind of semantic development from circumstance role marker to discourse unit must be typical for a class of lexical items and we plan to do some further research on it.