Stanley E. Porter and Matthew Brook O’Donnell 12 can be traced back through Halliday to the work of Firth 41. Firth’s work applied the theory of system (paradigmatic choices) and structure (syntag- matic choices) primarily to the phonological level of language 42. Halliday has extended Firth’s work to include both grammar and lexis. In fact, systemic linguistics rejects the traditional distinction between lexis (lexi- cal semantics treated in a lexicon) and grammar (morphological patterns discussed in grammar books). Instead, systemic theory talks about the lexicogrammar of language—that is, a continuum (or cline) of paradig- matic systems, with grammar (as traditionally described) at one end and lexis at the other 43. The fundamental concept of a system as a choice be- tween semantic features is present throughout the lexicogrammatical con- tinuum. Nevertheless, the systems at the grammatical end consist of a small, finite number of feature selections, and can thus be described as closed-systems, while systems at the lexis end consist of numerous sub- systems (consider, for instance, how many verbs of motion there are), and are described as open-systems. An example of a closed-system is the aspec- tual system in Hellenistic Greek (see section 3). There are at most four choices to be made by the language user who wishes to speak of a process, with the choice from a previous system becoming the entry condition for the next systemic choice: (1) a choice must be made with regard to the system of ASPECTUALITY (+expectational or +aspectual), (2) if the choice is +aspectual then the ASPECT1 system is the entry condition for the next choice (+perfective or –perfective), (3) if –perfective is selected then two further co-ordinated systems must be entered: (a) ASPECT2 becomes the entry condition for one set of choices (+imperfective or +stative) and (b) REMOTENESS for the other (–remote or +remote). It is clear how at each point an «either this or that» selection must be made, and that there are only a finite number of such choices, thus the aspectual system can be described as a closed-system. It should not be difficult to see how probabilities could be incorpo- rated into a systemic model of language 44. Given that for each system in a network a (usually) binary choice is made, then it is simply a matter of 41 See J.R. Firth, «A Synopsis in Linguistic Theory, 1930–1955», in J.R. Firth et al., Studies in Linguistic Analysis (Special Volume of the Philological Society; Oxford: Basil Blackwell, 1957), pp. 1-32. He notes that «the discussion of grammatical categories in closed systems for any given language» highlights the fact that «“meanings” are deter- mined by their inter-relations in the systems set up for that language» («Synopsis», p. 22). 42 See Firth, «Synopsis», pp. 17-22. 43 Halliday, «Corpus Studies and Probabilistic Grammar», p. 32; idem, «Language as System and Language as Instance», p. 63. Cf. R. Hasan, «The Grammarian’s Dream: Lexis as Most Delicate Grammar», in M.A.K. Halliday and R.P. Fawcett (eds.), New Developments in Systemic Linguistics. I. Theory and Description (London: Pinter, 1987), pp. 184-211. 44 Nesbitt and Plum suggest that «with choice as the basis of our theory of language, grammar can be modelled as sets of possibilities, as a potential for making meaning» («Probabilities and a Systemic-Functional Grammar», p. 7).