The Greek Verbal Network Viewed from a Probabilistic Standpoint 15 sess equiprobable and skewed systems is supported by the semiotic func- tion of language. If all of the systems where equiprobable, there would be no redundancy in the language and any interference («noise») would ham- per effective communication. On the other hand, if systems fell into a whole range of distributions, from 0.5/0.5 all the way up to 0.99/0.01 then the «semiotic system…would be virtually impossible to learn» 54. The language learner soon recognizes, and is thus able to master, systems where there is no unmarked term (equiprobable [0.5/0.5]) or where one term is highly marked in comparison to the other (skewed [0.9/0.1]) 55. Halliday uses the concept of markedness, as noted above, but does not define these categories, apparently opting for an intuitive understanding of the concept 56. As we have noted above, distributional markedness— along with material (morphological) markedness, implicational marked- ness and semantic markedness—was introduced and defined in Porter’s Verbal Aspect as a means of describing tendencies in Greek tense-form usage, although this was not pursued in detail. The concept of marked- ness was first introduced by Trubetzkoy 57, and then extended by Jakobson 58, in Prague-school linguistics to describe binary distinctive phonemic features or, by extension, distinctive conceptual features. According to this model, an item is marked if it displays this distinctive 54 Halliday, «Corpus Studies and Probabilistic Grammar», p. 36. 55 Halliday was given a chance to test this theory in a computerized language genera- tion project called the Penman project. He developed a grammar of English based on «a network of 81 systems each with a probability attached to the individual terms» (Halliday, «Language as System and Language as Instance», p. 65). He designated each system in the network as either equiprobable (probabilities 0.5/0.5) or skewed (0.9/0.1). This grammar was later named the «Nigel Grammar», after his son Nigel, who was the subject for his book Learning How to Mean: Explorations in the Development of Language (London: Edward Arnold, 1975). Describing the results of the grammar implemented in the Penman project, Halliday notes: «It was run as a random generator, without the probabilities attached; and it produced garbage as unconstrained grammar generators always do. But when it was run with the probabilities also being implemented, then (as the Director of the project, Bill Mann, expressed it to me afterwards) it produced gar- bage that now actually looked liked English—it bore some family resemblance to possi- ble human language» (Halliday, «Language as System and Language as Instance», p. 65). 56 See M.-L. Kean, «Markedness: An Overview», in W. Bright (ed.), International Encyclopedia of Linguistics (4 vols.; New York: Oxford University Press, 1992), II, pp. 390- 91, esp. p. 390: «In some work one finds precise definitions of markedness; elsewhere, the concept is taken as being antecedently well defined, or at least intuitively well understood.» 57 N. Trubetzkoy, «Die Aufhebung der phonologischen Gegensätze», Travaux du Cercle Linguistique de Prague 6 (1936), pp. 29-45; repr. in J. Vachek (ed.), A Prague School Reader in Linguistics (Bloomington: Indiana University Press, 1964), pp. 187-205. For an analy- sis of the fundamental concepts within their larger programme, see J. Vachek, The Linguistic School of Prague (Bloomington: Indiana University Press, 1966), esp. pp. 55-56. 58 R. Jakobson, «Zur Struktur des russischen Verbums», in Charisteria G. Mathesio (Prague: Cercle Linguistique de Prague, 1932), pp. 74-84; ET «Shifters, Verbal Categories, and the Russian Verb», in his Selected Writings. II. Word and Language (The Hague: Mouton, 1971), pp. 130-47.