#1588. The Uniformitarian Principle (3)[methodology][uniformitarian_principle]

　昨日の記事「#1587. 印欧語史は言語のエントロピー増大傾向を裏付けているか？」 ([2013-08-31-1]) で，Comrie による言語的エントロピー増加傾向の仮説を紹介した．Comrie の考え方の背景には，斉一論の原則 (The Uniformitarian Principle) の1つの解釈の仕方が関与している（斉一論については，「#556. The Uniformitarian Principle」 ([2010-11-04-1]) と「#1186. The Uniformitarian Principle (2)」 ([2012-07-26-1]) を参照）．
　言語における斉一論の原則について，いくつかの定義や説明を見てみると，言語の状態 (state) について述べているものと，言語の過程 (process) や力学 (force) について述べているものがある．例えば，[2010-11-04-1]の記事で挙げた引用に従えば，Romaine は force の斉一性を，Lass は state の斉一性を念頭においている（もっとも，Lass は "linguistic state of affairs (structure, inventory, process, etc.)" と包括的にとらえている節はある）．
　しかし，この2つの斉一論は大きく異なっている．state の斉一論は静態についての謂いであり，process/force の斉一論は動態についての謂いだ．後者は，現在と過去の言語変化の原動力や過程は異なるところがないと主張しているが，その結果としての言語状態については何も述べていない．極端にいえば，現在の言語と過去の言語が異なるタイポロジーを示すことすらありうるというのが，process/force の斉一論である．process/force の斉一論の主張者である Comrie (255--56) は，state の斉一論の主張者である Lass を批判する文脈のなかで，こう述べている．

In geology, certain processes can be observed as ongoing during recorded history, such as the formation of mountains and their subsequent erosion by wind and rain. The uniformitarian hypothesis, which did so much to raise geology to its present scientific level, assumes that these same processes also characterised the Earth's prehistory. In other words, in order to explain earlier geological formations, we are not permitted to appeal to processes other than those that have characterised the more recent period. But it is important to realise that what is constrained by the uniformitarian hypothesis is the set of processes that have formed the earth, not the set of states that are separated by these processes. Thus, one could imagine starting from a state that is radically different from the present state of the Earth, say a perfectly smooth spherical or near-spherical object, and then initiate operation of the processes of mountain formation and erosion to produce something like the present-day Earth. In other words, the typological consistency implied by the uniformitarian hypothesis in geology is a typological consistency of processes, not a typological consistency of states. . . . / We may now apply this historically more appropriate concept of uniformitarianism, from the viewpoint of the philosophy of science, to the kind of linguistic reconstruction that we proposed . . . . It now becomes clear that our reconstruction is indeed compatible with this conception of the uniformitarian hypothesis. We propose no processes that are not attested in the historical period. . . . No new types of processes are proposed. However, the operation of these processes can take us from an earlier stage that is typologically different from attested languages to a later stage that is compatible with our knowledge of attested language states.

　ここでは，地学主義とでもいうべき言語変化観が展開されている．state の斉一論なのか，process/force の斉一論なのか，あるいは両者を合わせた斉一論なのか．これもまた，controversial な議論である．

　・ Comrie, Barnard. "Reconstruction, Typology and Reality." Motives for Language Change. Ed. Raymond Hickey. Cambridge: CUP, 2003. 243--57.

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