Diachronic Development of Arabic Auxiliaries: A Corpus-Based Study Cursory synchronic review of the verb form raaHa 'leave, go' reveals unmistakable polyfunctionality. Making use of the standard grammaticalization theory in the analysis of diachronic coups data from pre-medieval times until the twentieth century, this paper argues that in Classical Arabic (CA) the andative (i.e., movement away from the speaker) sense of raaHa was primary and the emergent auxiliary-like function to an inceptive aspect marking on lexical verbs in 'doubly-inflected' verb periphrasis was minor (2.03%). A notable reversal of the functional status of raaHa was observed in Modern Standard Arabic (MSA) in the nineteenth and twentieth centuries, when roughly two thirds of its textual frequency was as an inceptive aspect marker, mostly in perfective/past inflection. Above and beyond its grammaticalization in CA/MSA, without inhibiting codification raaHa further grammaticalizes into an affix (e.g., raH- > Ha-) in a few modern dialects of Arabic (MDA), often in phonetically mutated forms (Levantine raH- > laH-, and Egyptian Ha- > ha-) that mark (1) unexpected and expected sequentiality; (2) deontic and epistemic modality; (3) futurity notions pertaining to intention, prediction, and simple future. Presenting a natural gradational grammaticalization pathway cutting across Arabic varieties, this paper further argues against the presumed discreteness of CA/MSA/MDA grammars. It relates synchronic polyfunctionality to diachronic continua, establishes the unevenness in the evolution of raH- in compared MDA, and hence suggests the non-inevitability of grammatical maturation for grammaticalizing elements. Finally, it proposes that maturation of auxiliaries in Arabic proceeds in MDA despite the socio-linguistic privileging of CA/MSA over MDA.