Induction models of constituency grammars or trees usually use data likelihood as both the objective and the model selection criterion (Seginer, 2007;Johnson et al., 2007;Ponvert et al., 2011;Shen et al., 2018), but the weak correlation between data likelihood and parsing accuracy hints at the non-optimality of this practice (Smith, 2006;Headden et al., 2009;Jin et al., 2018a).
many linguistic and psycholinguistic theories propose constraints either as properties of natural language grammar or as constraints on human processing and acquisition.