This paper explores desiderative modals such as beʔ^4, ai^3 and negative words such as m^7, bo^5 and bue^7/be^7 with respect to their individual semantic properties and the meanings that arise in combination with other words. As attested in authentic data, the interpretations of these words have an intimate relationship with the constructions in which they occur. A finding in this paper is that asymmetric relation between form and meaning is shown in monosyllabic words such as beʔ^4, ai^3 and m^7, whereas when they are changed into disyllabic words the meaning becomes more explicit and less susceptible to ambiguity. As a result, earlier monosyllabic and newly developing disyllabic words form a picture of coexistence and even competition.