This and similar behaviour in other Salish and Wakashan languages has been used as evidence for a complete lack of a lexical distinction between nouns and verbs in these families. This has become controversial in recent years. David Beck of the University of Alberta contends that there is evidence for distinct lexical categories of 'noun' and 'verb' by arguing that, although any distinction is neutralised in predicative positions, words that can be categorised as 'verbs' are marked when used in syntactic argument positions. He argues that Salishan languages are omnipredicative, but only have 'uni-directional flexibility' (not 'bi-directional flexibility'), which makes Salishan languages no different from other omnipredicative languages such as Arabic and Nahuatl, which have a clear lexical noun-verb distinction.