#1303. なぜ方言が存在するのか --- 波状モデルによる説明[dialect][family_tree][wave_theory][geography][isogloss][dialect_continuum][sobokunagimon]


 昨日の記事「#1302. なぜ方言が存在するのか --- 系統樹モデルによる説明」 ([2012-11-19-1]) に引き続き,なぜ方言が存在するのか,なぜ方言が生まれるのかという素朴な疑問に迫る.昨日述べた系統樹モデル (family_tree) による説明の欠陥を補いうるのが,波状モデル (wave_theory) だ.
 Bloomfield (317) の記述を借りて,波状モデルによる方言分化の説明としよう.

Different linguistic changes may spread, like waves, over a speech-area, and each change may be carried out over a part of the area that does not coincide with the part covered by an earlier change. The result of successive waves will be a network of isoglosses . . . . Adjacent districts will resemble each other most; in whatever direction one travels, differences will increase with distance, as one crosses more and more isogloss-lines. This, indeed, is the picture presented by the local dialects in the areas we can observe.

 ここで前提とされているのは,(1) 言語変化(言語的革新)が次々と生じ,波状に拡散することと,(2) 個々の言語変化によって波の到達範囲が異なることだ.この2点により,方言地理のカンバスには,複雑に入り組んだ等語線 (isogloss) が引かれることになる.任意の2地点をとると,互いに近ければ近いほど,過去の言語変化を多く共有しているので,全体として言語的な共通点が多く,近い方言を話すことになる.逆に遠ければ遠いほど,歴史的に共有してきた言語変化は少ないので,全体として違いの大きい方言を話すことになる.後者のケースでは,時間が経てば経つほど,言語的な共通点が少なくなり,最終的には互いに通じない異なる言語へと分化してゆく.
 Bloomfield (317--18) は上の引用に続けて,波状モデルによる方言分化について,より突っ込んだ理論的な視点から解説を与えている.こちらも引用しておこう.

Now, let us suppose that among a series of adjacent dialects, which, to consider only one dimension, we shall designate as A, B, C, D, E, F, G, . . . X, one dialect, say F, gains a political, commercial, or other predominance of some sort, so that its neighbors in either direction, first E and G, then D and H, and then even C and I, J, K, give up their peculiarities and in time come to speak only the central dialect F. When this has happened, F borders on B and L, dialects from which it differs sharply enough to produce clear-cut language boundaries; yet the resemblance between F and B will be greater than that between F and A, and, similarly, among L, M, N, . . . X, the dialects nearest to F will show a greater resemblance to F, in spite of the clearly marked boundary, than will the more distant dialects. The presentation of these factors became known as the wave-theory, in contradistinction to the older family-tree theory of linguistic relationship. Today we view the wave process and the splitting process merely as two types --- perhaps the principal types --- of historical processes that lead to linguistic differentiation.

 ・ Bloomfield, Leonard. Language. 1933. Chicago and London: U of Chicago P, 1984.

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