The Oxford Dictionary of English Grammar
The present subjunctive form of a verb is finite, and identical with the base form of the verb. Formally, it is exactly the same as the present tense indicative form, except for the third person singular, which lacks -s, and for the verb be, whose present subjunctive form is be.... First, the mandative subjunctive.... I recommended that he write and apologize.... This is called the should-mandative in CaGEL, and putative should in CGEL.
その後に仮定法過去の説明が続くのですが...：
The Oxford Dictionary Of English Grammar
The so-called past subjunctive (also called the were-subjunctive or irrealis were) is used in clauses of hypothetical condition. It differs from the past indicative form of be only in the first and third person singular, where were is used, though was is increasingly found here too. The reference is to present (or future) time, e.g.
- If I were you, I'd own up (compare: If I was you...)
- If only my grandfather were alive today (compare: If only my grandfather was...)
- If she were to come tomorrow...(compare: If she was to...)
書き出しから「いわゆる仮定法過去（the so-called past subjunctive）」となっていて、これがbe動詞のwereを用いるものに限定されるとしています。仮定法は元々は動詞の語形を「仮定形（subjunctive form）」にすることで表すものとされているので、明らかに仮定法でのみ使用されるwereのみが仮定法に分類されているわけです（同じく仮定法現在も仮定形として原形不定詞を用いたもののみが厳密な意味での「仮定法」になり、shouldを用いるものは意味的には同じでも別分類になっています）。
『The Oxford Dictionary of English Grammar』では、一般動詞の過去形を用いる場合は「仮定法過去」ではなく過去形の特殊な用法として分類されています：
The Oxford Dictionary Of English Grammar
past 2. (A tense or inflectional form of a verb)
typically expressing anteriority. The grammatical label past tense is typically used of a verb form that refers to a situation that took place in the past. However, this association can be misleading. While the past tense typically refers to past time, it can also be used hypothetically. To put it differently, it can denote modal remoteness (hence the alternative labels hypothetical past, modal past, and modal preterite), i.e. mark unreality, non-factuality, and so on:
- If I had my way, I would abolish this organization
- I wish I knew
The past tense can also be used for social distancing (the attitudinal past):
- Could you lend me some money?
- I wanted to ask you something
『The Cambridge Encyclopedia of the English Language』でも、過去形の「時間的過去」以外を意味する用法の中において、仮定法過去に相当する用法に言及しています：
The Cambridge Encyclopedia of the English Language
TENSES
One of the most important functions of the verbs is to indicate the time at which an action takes place....
PAST TENSE
Most uses refer to an action or state which has taken place in the past, at a definite time, with a gap between its completion and the present moment. Specific events, states, and habitual actions can all be expressed with this tense: I arrived yesterday (event), They were upset (state), They went to work every day (habitual).
The past tense is also used for present or future time.
The attitudinal past reflect a tentative state of mind, giving a more polite effect than would be obtained by using the present tense: Did you want to leave? (compare the more direct Do you want to leave?)
The hypothetical past expresses what is contrary to the speaker's beliefs: I wish I had a bike (i.e. I haven't got one). It is especially used in if-clause.
In indirect speech, a past tense used in the verb of 'saying' allows the verb in the reported clause to be past tense as well, even though it refers to present time: Did you say you had no money? (i.e. you haven't any now)（p.236）.
つまり、「過去時制（past tense）」は、過去の行為や出来事を表す以外に①仮定的過去（hypothetical past、仮定法過去に相当）、②丁寧表現、③間接話法における時制の一致（backshift）において用いられるとあります。①の用法を仮定「法」という分類にはしないわけです。
英語圏で英語学習者用に広く用いられているCambridge出版の教科書『Grammar Use in Use』にも、以下のように書かれています：
Advanced Grammar Use in Use
The subjunctive is a set of verb forms used mainly in rather formal English to talk about possibilities rather than facts. The present subjunctive uses the base form of the verb (e.g. We suggest that she leave immediately) and the past subjunctive uses were (e.g. If I were you, I'd go home now) (p.209).
同じく英語圏で英語学習者用に広く用いられているOxford出版の文法書『Practical English Usage（ＰＥＵ）』には以下のように書かれています：
Practical English Usage
567 subjunctive
1 What is the subjunctive?
Some languages have special verb forms called 'subjunctive', which are used especially to talk about 'unreal' situations: things which are possible, desirable or imaginary. Older English had subjunctives, but in modern English they have mostly been replaced by uses of should, would and other modal verbs, by special uses of past tenses (see 426), and by ordinary verb forms. English only has a few subjunctive forms left: third-person singular present verbs without -(e)s, (e.g. she see, he have) and special forms of be (e.g. I be, he were). Except for I/he/she/it were after if, they are not very common.
426 past verb form with present or future meaning
A past tense does not always have a past meaning. In some kinds of sentence we can use verbs like I had, you went or I was wondering to talk about the present or future.
1 after conjunctions, instead of would
In most subordinate clauses (e.g. after if, supposing, wherever, what), we use past tenses (and not would...) to express 'unreal' or conditional ideas (see 580.6).
- If I had the money now I'd buy a car....
- I wish (that) I had a better memory.
We can make questions, requests and offers less direct (and so more polite) by using past tenses. (For more about 'distancing' of this kind, see 436.) Common formulae are I wondered, I thought, I hoped, did you want.
- I wondered if you were free this evening.
- I thought you might like some flowers.
- Did you want cream with your coffee, sir?
- I was thinking about that idea of yours.
- I was hoping we could have dinner together.
The 'past' modal forms could, might, would and should usually have present or future reference; they are used as less direct, 'distanced' forms of can, may, will and shall.
- Could you help me for a moment?
- Would you come this way, please?
- I think it might rain soon.
- Alice should be here soon.
仮定法を動詞の活用だけに限定してしまうと、英語においては明白な仮定法専用の活用形が存在しないため、「be動詞wereの場合だけ仮定法で一般動詞の場合は過去時制の特殊な用法」などという何ともややこしい話になってしまいます。それで、「仮定（subjunctive）」は、動詞の単なる語形変化（subjunctive form）ではなく構文（subjunctive construction）として捉えようとされてきているようです。
The Oxford Dictionary of English Grammar
However, since Modern English (unlike, say, French or Spanish) has few distinct verb forms that differentiate subjunctive verb forms from indicative verb forms, the status of the subjunctive as a verbal inflection has been challenged. Indeed, many modern frameworks prefer to speak of subjunctive constructions or subjunctive clauses. These labels then apply to the entire clause in which the 'subjunctive verb' appears.
The Cambridge Grammar of the English Language
The general term subjunctive is primarily used for a verbal mood that is characteristically associated with subordinate clauses with a non-factual interpretation. We are extending the term so that it applies to a syntactic construction rather than a verb-form, but our subjunctive clauses are still characteristically subordinate and non-factual. We need a different term for 1st/3rd person singular were: we call it irrealis, a general term applying to verb moods associated with unreality (i.e. where the proposition expressed is, or may well be, false).
語形変化などによって表される「mood（法）」は、canやmustなどの法助動詞（modal verbs）によって表されるものも含めた「法性（modality）」表現の広いくくりの中の、特殊な（半ば廃れがちな）一区画的扱いになるようです。
法：文法範疇の一つ。定動詞の語形替変として現れ，文の内容に対する話者の心的態度を示す。ギリシア語などの古典文法に由来する概念で，たとえばギリシア語には，直説法，接続法，希求法，命令法の4つの法があった。近代のインド＝ヨーロッパ語族の諸言語では，動詞の活用組織が簡略になったり，助動詞を用いる分析的表現が多くなったりして，動詞の替変形から定義されるものとは必ずしもいえない言語もある。
いずれにしろ、英語圏の英語学習者用教材では、仮定法過去は「仮定法」という文法項目として一つの大きな章で扱われることは少ないようです。多くの場合、if条件文の一種的な扱いです：
The Oxford Dictionary of English Grammar
Simplified grammar books for foreign learners often classify conditional constructions into three types according to the tense forms used:
- first conditional (also called the will-condition): involves a present tense verb form in the conditional clause, and will in the main clause, e.g. If I see them, I will tell them
- second conditional (also called the would-condition): involves a past tense verb form in the conditional clause, and would in the main clause, e.g. If I saw them, I would tell them
- third conditional (also called the would have-condition): involves a past perfect in the conditional clause, and would have in the main clause, e.g. If I had seen them, I would have told them
Practical English Usage
258 if (3): special structures with past tenses and would
1 unreal situations
We use special structures with if when we are talking about unreal situations--things that will probably not happen, situations that are untrue or imaginary, and similar ideas. In these cases, we use past tenses and would to 'distance' our language from reality.
2 if+past; would+infinitive without to
To talk about unreal or improbable situations now or in the future, we use a past tense in the if-clause (even though the meaning is present or future), and would+infinitive (without to) in the other part of the sentence.
- If I knew her name, I would tell you.....
We often use were instead of was after if. This is common in both formal and informal styles. In a formal style were is more common than was, and many people consider it more correct, especially in American English. The grammatical name for this use of were is 'subjunctive' (see 567).
- If I were rich, I would spend all my time travelling.
- If my nose were a little shorter I'd be quite pretty.
1 if + past perfect; would have + past participle
To talk about past situations that did not happen, we use a past perfect tense in the if-clause, and would have + past participle in the other part of the sentence.
- If you had asked me, I would have told you.
「仮定法」の項目がある場合には仮定法現在が主に扱われ、その中でついで的に仮定法過去についても言及されることがある程度です。ドーンと大きく「仮定法」の項目がある日本の英語学習教材と比べるとかなり異なる扱いです。
