This paper presents the first qualitative analysis of the Czech causal construction protože X ‘because X’. First, against the backdrop of a number of earlier analyses of equivalent constructions in English, German, and Dutch, the article discusses the variability of the X slot of the Czech construction. Second, it is argued that although some instances of the construction are definitely elliptical, others are not, and generally categorising protože X as a case of ellipsis is therefore inadequate. The crucial distinction is made between reconstructing an ellipsis and expanding a non-ellipsis. Third, a brief sketch of the diachrony of the construction is presented. It is suggested that non-elliptical protože X constructions developed out of elliptical clauses with protože ‘because’. These elliptical instances of protože X can be found as early as in the 19th century. Finally, the Czech construction protože X is compared with its equivalents in English, German, and Dutch. Finally, further research questions are suggested.