This paper proposes a theoretical, methodological and descriptive framework for combining a gestural-mimetic theory of the sign with the principle of arbitrariness. First, it draws attention to the history of the question, discusses its theoretical core and presents a method to analyse the relationship between the differential system of phono-articulatory signifiers and the differential system of logical-semantic signifieds. In section 2, this method is tested on the Italian grammatical monosyllables, focusing on a complete description of the words formed from one phoneme (‘monophonemes’), of the words distinguishing grammatical persons and of the adverbial pairs. The main result is that phono-articulatory oppositions (such as [open : closed] and [front : back]) can be systematically described as images of logical-semantic oppositions (such as {complex : simple} and {positive : negative}, respectively). In section 3, a number of conclusions are drawn, particularly about the difference between linguistic ‘values’ and psychological ‘concepts’.