Over the past decade dialogue between Systemic Functional Linguistics and Legitimation Code Theory about the nature of knowledge (Christie & Martin, 2007; Christie & Maton, 2011) has rekindled interest among the linguists involved in the register variable field (e.g. Martin, 2007; Martin et al., 2010). More recently, as part of an interdisciplinary project focusing on knowledge building in secondary school history and science lessons (Freebody et al., 2008; Martin & Maton, 2013), Maton\u27s work on semantic gravity (Maton in press) has rekindled interest in mode