hellog〜英語史ブログ / 2015-08-13

■ #2299. 拡散の駆動力3点 [lexical_diffusion][language_change][causation][analogy][schedule_of_language_change]

　言語変化の拡散 (diffusion) のメカニズムについて，合理的な観点から「#1572. なぜ言語変化はS字曲線を描くと考えられるのか」 ([2013-08-16-1])，「#1642. lexical diffusion の3つのS字曲線」 ([2013-10-25-1])，「#1907. 言語変化のスケジュールの数理モデル」 ([2014-07-17-1])，「#2168. Neogrammarian hypothesis と lexical diffusion の融和 (2)」 ([2015-04-04-1]) を中心に，lexical_diffusion の各記事で扱ってきた．
　拡散の駆動力が何であるかという問いに対して，Denison (58) は変異形の選択にかかる圧力という答えを出しているが，De Smet (8) は主たる原動力は類推作用 (analogy) であり，それに2つの補助的な力が加わっていると考えている．まず，主力である類推作用から見てみよう．

Most innovations in diffusion appear to arise through analogy---that is, as a result of the bearing out of synchronic regularities. There are two reasons analogy can lead to unidirectional diffusion of a pattern. If we assume that analogy is sensitive to frequency, in that analogical pressure grows as the analogical model becomes more frequent, it follows that as diffusion proceeds analogy grows stronger and more and more environments will yield to its pressure. In this sense, diffusion is a self-feeding process, keeping itself going once it has been triggered. . . . But analogy can be self-feeding not only in a quantitative but also in a qualitative way. . . . [D]iffusion can proceed along analogical chains, whereby every actual change reshuffles the cards for any potential change. Because language users are tireless at inferring regularities from usage---and may even not mind some degree of inconsistency---each analogical extension changes the generalizations that are likely to be inferred, opening new horizons to further analogical extension.

　ここで提案されている変異形の頻度という要因を含むメカニズムは，Denison の述べる変異形の選択にかかる圧力にも近い．しかし，言語変化の拡散は，類推というメカニズムが機械的に作用することによってのみ駆動されているわけではない．類推が主たる原動力となりつつも，個々の変異に補助的で局所的な力が働き，拡散の経路が「補正」されるという考え方だ．De Smet (8) によれば，その補助的な力は2種類ある．

Nevertheless, it would be simplistic to believe that analogical snowballs and chains operate exclusively on the basis of analogy. I see at least the following two auxiliary factors. First, if linguistic choices are determined by multiple and variable considerations that are weighed against each other, every usage event comes with a unique constellation of factors pulling linguistic choices one way or another. It is therefore inevitable that there are occasional contexts in which language users are strongly compelled to go against the default grammatical regularities of the system. The unusual choices that occasionally arise in this way may help break down resistance to change. Second, the construction from which a new spreading pattern derives usually occurs in a number of different environments. Because of this, the new pattern is present from the very start in a number of different places in the system, having as it were a diffusional headstart that can very quickly lead to the inference of new generalizations.

　補助的な力の1つは，個々の変異の選択に働く諸要因の複雑な絡み合いそのものである．個々の変異をとりまく環境がすでに1つの小体系を成しており，大体系や他の小体系からの独自性をもっている．小体系のもつこの独自性は，ときに大体系のもつ安定性に抵抗し，言語変化の原動力となるだろう．2つめは，刷新形は当初から様々な環境において現われるという事実だ．このことは，初期段階から拡散が進んでいくはずの環境がある程度きまっているということでもあり，拡散を駆動する力につながるだろう．2つの補助的な力は，類推という主たる駆動力を裏で支えているものと考えることができそうだ．

　・ Danison, David. "Log(ist)ic and Simplistic S-Curves." Motives for Language Change. Ed. Raymond Hickey. Cambridge: CUP, 2003. 54--70.
　・ De Smet, Hendrik. Spreading Patterns: Diffusional Change in the English System of Complementation. Oxford: OUP, 2013.

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