Krebernik and Streck, in their 2001 study on irrealis, also suggested that tuša is connected to tuššum, noting that the etymology of the latter noun is still enigmatic, […] Furthermore, they postulate the possibility of a nominalization of the particle into the noun tuššum. Looking at the question from a wider angle, one finds that in different languages MPs tend to acquire their function by a process of grammaticalization, starting as regular lexical items (noun, adverbs, conjunctions) and then become MPs.