Relative pronouns i-/je- and restrictive particle -le became conflated in concessive conditionals (e.g. No matter how much financial support we get, we will go ahead with our project). This syntactic environment explains why Old Polish ile functioned in the oldest Polish texts as an indefinite pronoun ‘no matter how much’ (a so- -called free choice determiner). The present paper aims to show in which way the historical syntax may enrich our knowledge on etymology and language changes.