Case study: the evolution of must
Having set out the path of change predicted by Invited Inferencing Theory, we now consider a case study of grammaticalisation discussed by Traugott and Dasher (2002). Traugott and Dasher observe that modal verbs (see Chapter 18) follow a unidirectional path of evolution. Firstly, content expressions evolve into deontic modals which express obligation, permission or prohibition (e.g. George must learn to be on time). The same expressions then evolve into epistemic modals which relate to knowledge and belief (e.g. George must be home by now). Evolution in the opposite direction (from content expression to epistemic to deontic) is not attested. Secondly, the path of evolution is from narrow scope (over some subpart of the proposition) to wide scope (over the whole proposition), not vice versa. This point is illustrated below. Finally, this path of grammaticalisation correlates with increased subjectivity. The properties that characterise the evolution of modal verbs are summarised in Table 21.3.
In order to illustrate this path of evolution, Traugott and Dasher present a case study of the English modal must. In Modern English, this modal verb has both deontic readings (16a) and epistemic readings (16b).
Traugott and Dasher describe the evolution of this verb from Old English to Modern English in terms of three stages:
As these examples demonstrate, must originated in Old English as a content verb meaning ‘be able’ and evolved into a deontic verb expressing permission and then obligation (19). Traugott and Dasher (2002) argue that the evolution from permission to obligation correlates with increased subjectivity. The earliest uses of the obligation (deontic) sense of must appear to have been participant-external. That is, the obligation (deontic) sense arose in contexts where permission was being granted to a third person referent. In such contexts, particularly when
the person or entity granting the permission, such as a King or the Church, is in a position of authority, there is a context-induced implication of obligation. Once the deontic sense was established, more subjective participant-internal (first person) uses began to emerge, as illustrated by the example in (19). The shift from deontic to epistemic senses in (20)–(21) also follows a path from objective to subjective uses. According to Traugott and Dasher (2002: 132), therefore, there is no basis for a metaphorical account of the evolution of this modal verb since an invited inferencing analysis provides an explanatory account.
In summary, the main claim of Invited Inferencing Theory is that contextual (pragmatic) meaning is reanalysed as inherent (coded) meaning. While the role of metaphor is recognised, it is not seen as the central force behind the grammaticalisation process.
