AbstractThe Greek documentary papyri (300 bce – 700 ce) provide an interesting corpus for linguistic study due to the large amount of linguistic variation. Variation in spelling is traditionally used as evidence for phonological changes in the post‐Classical Greek language. The interchange of graphemes, however, does not only depend on the pronunciation of the corresponding phoneme. In this paper I examine the cognitive processes behind the production of non‐standard Greek orthography in more detail by applying an interactive dual‐route model for spelling. If two graphemes are pronounced identically in the spoken language, the final choice between one grapheme or the other is likely to be based on cognitive and social aspects, such as the general frequency and probability of spelling patterns in the language, previous exposure of the writer to other lexemes and morphemes in the language and local scribal conventions, to name just a few factors. On the basis of examples of the frequent interchanges of <e, ai> and <o, ō>, I show how these other factors can contribute to a better interpretation of spelling production in documentary papyri.