Arabic syntax has yet to be studied in detail from a corpus-based perspective. The Arabic copula kāna, ‘be’, functions additionally as an auxiliary, creating periphrastic tense-aspect constructions; but the literature on these functions is far from exhaustive. To analyse kāna within the million-word Leeds Corpus of Contemporary Arabic, part-of-speech tagging (using novel, targeted enhancements to a previously described program which improves the accessibility for linguistic analysis of the output of Habash et al.’s 2012 MADA disambiguator for the Buckwalter Arabic morphological analyser) is applied to disambiguate copula and auxiliary at a high rate of accuracy. Concordances of both are extracted, and 10% samples (499 instances of copula kāna, 387 of auxiliary kāna) are manually analysed to identify surface-level grammatical patterns and meanings. This raw analysis is then systematised according to the more general patterns’ main parameters of variation; special descriptions are developed for specific, apparently fixed-form expressions (including two phraseologies which afford expression of verbal and adjectival modality). Overall, substantial new detail, not mentioned in existing grammars, is discovered (e.g. the quantitative predominance of the past imperfect construction over other uses of auxiliary kāna); there exists notable potential for these corpus-based findings to inform and enhance not only grammatical descriptions, but also pedagogy of Arabic as a first or second/foreign language.