This paper offers a distributional account of the morphology and semantics of the Old Arabic relativizers llaḏī, ḥayṯu, man/mā-min, showing that they constitute a multi-layered pattern of complementary distribution, based on the semantic opposition {-/+restrictive}, and on its audible counterpart. Far from being a suprasegmental opposition {+/-pause} (cp. English), the latter opposes lla, ḥay to min, which are analyzed accordingly as replacive morphemes of {+/-pause}. Such a replacive allomorphy is also given a pragmatic characterization, and explained as an adaptive behavior of Old Arabic, relative to its oral-poetic ecological conditions. Deviations from the aforesaid pattern are explained here by invoking typological factors such as heaviness and Jespersen cycle which, in turn, are triggered by an instance of phonological reduction described by Arab Grammarians, and targeting min. This phenomenon is arguably part and parcel of a more general shift from analytical to synthetical language, well-known to typologically-oriented studies on (Old) Arabic.1 This paper is based on some materials presented at the 4th Congress of the Coordinamento dei Dottorati Italiani in Scienze Cognitive (Rome, June 7-9, 2010) and the 26th Congress of the Union Européenne des Arabisants et Islamisants (Basel, September 12-16, 2012). It ideally complements the research on Old Arabic relative markers and clauses carried out in Grande (2013: Chs. 2, 3), but can be read independently of it. Abbreviations