The article examines the origin and functional development of the Slavic conjunction ače ‘if; although’ (OPol. acz). The marker of the protasis in conditional clauses was the enclitic *-če, which continues the function of IE *-kʷe ‘and; if’. Thus, Sl. *-če ‘if’ is an archaism and may be compared with corresponding forms in Indo- ranian, Hittite, and Latin. The concessive ače ‘although’ evolved from conditional concessive clauses. The proposed interpretation also sheds light on the genesis of OCz. leč ‘if only’.
