昨日の記事「#5456. 主語とは何か？」 ([2024-04-04-1]) に引き続き，主語 (subject) についての本質的な疑問に迫りたい．この問題を論じるに際し，まず用語辞典などに当たってみるのが良さそうだ．McArthur の項目を引用しよう．主要な論点が見えてくる．
SUBJECT [13c: from Latin subjectum grammatical subject, from subiectus placed close, ranged under]. A traditional term for a major constituent of the sentence. In a binary analysis derived from logic, the sentence is divided into subject and predicate, as in Alan (subject) has married Nita (predicate). In declarative sentences, the subject typically precedes the verb: Alan (subject) has married (verb) Nita (direct object). In interrogative sentences, it typically follows the first or only part of the verb: Did (verb) Alan (subject) marry (verb) Nita (direct object)? The subject can generally be elicited in response to a question that puts who or what before the verb: Who has married Nita?---Alan. Where concord is relevant, the subject determines the number and person of the verb: The student is complaining/The students are complaining; I am tired/He is tired. Many languages have special case forms for words in the subject, the subject requires a particular form (the subjective) in certain pronouns: I (subject) like her, and she (subject) likes me.
Kinds of subject. A distinction is sometimes made between the grammatical subject (as characterized above), the psychological subject, and the logical subject: (1) The psychological subject is the theme or topic of the sentence, what the sentence is about, and the predicate is what is said about the topic. The grammatical and psychological subjects typically coincide, though the identification of the sentence topic is not always clear: Labour and Conservative MPs clashed angrily yesterday over the poll tax. Is the topic of the sentence the MPs or the poll tax? (2) The logical subject refers to the agent of the action; our children is the logical subject in both these sentences, although it is the grammatical subject in only the first: Our children planted the oak sapling; The oak sapling was planted by our children. Many sentences, however, have no agent: Stanley has back trouble; Sheila is a conscientious student; Jenny likes jazz; There's no alternative; It's raining
Pseudo-subjects. The last sentence also illustrates the absence of a psychological subject, since it is obviously not the topic of the sentence. This so-called 'prop it' is a dummy subject, serving merely to fill a structural need in English for a subject in a sentence. In this respect, English contrasts with languages such as Latin, which can omit the subject, as in Veni, vidi, vici (I came, I saw, I conquered: with no need for the Latin pronoun ego, I). Like prop it, 'existential there' in There's no alternative is the grammatical subject of the sentence, but introduces neither the topic nor (since there is no action) the agent.
Non-typical subjects. Subjects are typically noun phrases, but they may also be finite and non-finite clauses: 'That nobody understands me is obvious'; 'To accuse them of negligence was a serious mistake'; 'Looking after the garden takes me several hours a week in the summer.' In such instances, finite and infinitive clauses are commonly post and anticipatory it takes their place in subject position: 'It is obvious that nobody understands me'; 'It was a serious mistake to accuse them of negligence.' Occasionally, prepositional phrases and adverbs function as subjects: 'After lunch is best for me'; 'Gently does it.'
Subjectless sentences. Subjects are usually omitted in imperatives, as in Come here rather than You come here. They are often absent from non-finite clauses ('Identifying the rioters may take us some time') and from verbless clauses ('New filters will be sent to you when available'), and may be omitted in certain contexts, especially in informal notes (Hope to see you soon) and in coordination (The telescope is 43 ft long, weighs almost 11 tonnes, and is more than six years late).
項目の書き出しは標準的といってよく，おおよそ文法的な観点から主語の概念が導入されている．主部・述部の区別に始まり，主語の統語論的振る舞いや形態論的性質が紹介される．
次の節では，主語が文法的な観点のみならず心理的，論理的な観点からもとらえられるとして，別のアングルが提供される．心理的な観点からは「テーマ，主題」，論理的な観点からは「動作の行為者」に対応するのが主語なのだと説かれる．現実の文に当てはめてみると，3つの観点からの主語が必ずしも互いに一致しないことが示される．
続けて，擬似的な主語，いわゆる形式主語やダミーの主語と呼ばれるものが紹介される．そこでは there is の存在文 (existential_sentence) も言及される．この構文では there はテーマではありえないし，動作の行為者でもないので，あくまで文法形式のために要求されている主語とみなすほかない．
通常，主語は名詞句だが，それ以外の統語カテゴリーも主語として立ちうるという話題が導入されたあと，最後に主語がない（あるいは省略されている）節の例が示される．
ほかにも様々に論点は挙げられそうだが，今回は手始めにここまで．
・ McArthur, Tom, ed. The Oxford Companion to the English Language. Oxford: OUP, 1992.
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