Abstract
The paper describes the development of selected Czech modal words expressing epistemic modality, like ovšem, určitě, samozřejmě, jistě, zajisté 'yes, sure, of course' and možná, snad, třeba 'maybe, perhaps, possibly'. In the diachronic point of view, attention is paid mainly to the period between 1800 and 1945.
The mentioned words lose their original part of speech function, modify the whole utterance and are used as means for discourse control and for the structuration of verbal communication in this new function. By their constitution processes, which lead to emphasizing their pragmatical function, following criteria are met: semantic bleaching, syntacticalization, decategorization; i. e. in the delimitation of these units, similar developments appear as with grammaticalization and/or lexicalization.