In the Arabic linguistic tradition, the classification of the parts of speech (ism ‘noun’, fiʿl ‘verb’, ḥarf ‘particle’) is first introduced by Sībawayhi, who presents the three key elements in his Kitāb (I:1). The section at issue includes the presentation of the elements but does not provide much in terms of grammatical explanation. Nouns are in fact not introduced with their grammatical characteristics, but rather with examples: fa-l-ism: raǧul, wa-faras, wa-ḥāʾiṭ (“and the noun is ‘man’, and ‘horse’, and ‘wall’”) (Kitāb I:1). In addition to nouns, verbs and particles, Arabic grammar further recognized a number of other categories that are not considered as parts of speech but rather fall into the main three. This contribution aims to present relevant classifications of the parts of speech in the Greek and Arabic traditions, with the aim to account for possible external influences on the Arabic formulations, and foster further discussion on the development of the Arabic grammatical disciplines.