A Modern English Grammar on Historical Principles (MEG) is a seven-volume reference grammar of Modern English, largely written by Otto Jespersen. The first volume ("part"), Sounds and Spellings, was published in 1909; two through five were on syntax; six was on morphology; and seven returned to the topic of syntax. It took until 1949 for all seven to be completed.

Aim and scope The appearance of MEG seems to have been expected. The largely unenthusiastic reviewer of Jespersen's Progress in Language wrote in 1895:

I must close this notice with the expression of the hope that Prof. Jespersen will continue his investigations of special points in English grammar and will give us a systematic treatise on the subject. He has adopted the only fruitful way, the collection of historical examples and the deduction of conclusions from them by examination and comparison.

A history of linguistics in the Nordic countries describes MEG in retrospect:

The most outstanding, and without doubt the most influential of the Danish contributions to descriptive grammar was Otto Jespersen's [MEG] (1909–1949). . . . [A]lthough it is certainly not untouched by the neogrammarian education of its author, it is mainly a descriptive study illustrating Jespersen's general ideas of descriptive linguistics. . . .

MEG is "[a] monumental seven-volume grammar of English" that emerged around the same period as did two other multivolume reference grammars of English, both by Dutch scholars: Etsko Kruisinga's A Handbook of Present-Day English (1909–1932), and Hendrik Poutsma's A Grammar of Late Modern English for the Use of Continental, Especially Dutch, Students (1904–1926). In each of these three, the author "used thousands of examples from literary texts to illustrate points of grammar".

Similarly to MEG, Kruisinga's Handbook starts with a volume on phonology and orthography, but, unlike MEG or Poutsma's work, "[has] no historical pretensions". By contrast, MEG – whose author wrote elsewhere that "The distinctive feature of the science of language as conceived nowadays is its historical character" – delivers on its promise of "historical principles".

MEG is unlike the other pair in another way. American English "does not figure in [Poutsma's Grammar] to any significant extent", and is similarly uncommon in Kruisinga's Handbook. By contrast, in MEG, "the total number of comments on [American English] amounts to 224, of which 50 are on phonology (including stress), 9 on spelling, 83 on morphology and syntax, 64 on lexical items, and 18 on word-formation". Those on syntax include a discussion (MEG IV:260–261) on shall versus will in American English.

Jespersen propounded the system underpinning MEG in his book The Philosophy of Grammar (1924).

Part by part The work was eventually published in a total of seven of what would normally be termed volumes. But the term part was largely used instead (and volume used additionally for four of those five parts concerned with syntax).

Part I. Sounds and Spellings This first installment was first published in 1909. (For a more detailed publishing history of this and the other parts, see "Publishing details" below.)

The chapters are:

Corrections were made for the 1949 edition.

Part II. Syntax (first volume) This was first published in 1914. Although Jespersen might have been expected to proceed from phonology and orthography to syntax via morphology, he postponed morphology, explaining that the prospect of dealing with syntax was more enticing and there was a greater demand among his friends for reading his ideas on syntax.MEG II:v; quoted in .

In his preface, Jespersen describes his system of exemplification and citation, "collected during many years of both systematic and desultory reading" (MEG II:vi); most of this is unremarkable, but:

In quotations from works of fiction I have now and then abbreviated a proper name or replaced it by he or she, just as I have here and there left out a few unimportant words; but I have taken such liberties only with quotations from recent books and where I was quite sure that they could in no wise impair the value of the passage for the purpose for which I used it. (MEG II:vii)

The chapters are:

Later editions add an appendix presenting additions and commentary by Jespersen; for the 1949 edition, Niels Haislund added pointers in the main text to this appendix.

Part III. Syntax (second volume) First published in 1927. The chapters of a later edition – "Reprinted in Great Britain 1961" and lacking any acknowledgment of revision – are:

"(Appendix to Volume III) Predicatives after particles" appeared as the final (23rd) chapter of Part IV.

A detailed review of Part III by Martin B. Ruud starts by saying that a grammarian "must be a realist, a philosopher, an historian, even an antiquarian, and something of an artist as well", and that Jespersen here again demonstrates these qualities. The review then describes particular chapters, or sequences thereof. Of chapter 2, Ruud introduces Jespersen's novel term content clause and describes Jespersen's distinction between X questions and nexus questions (roughly corresponding to what are now more commonly termed open interrogative and polar interrogative clauses respectively). He is glad that Jespersen: "continues to oppose resolutely . . . the use of the term 'dative' in Modern English", commenting: "indeed, where there are no criteria of form how can one speak of something that is either form or nothing at all?" Ruud then considers how the book illuminates lexicological matters, such as the common confusion of intransitive lay and transitive lie – Jespersen does not condemn this (made by authors such as Marvell, Byron and Emily Brontë, it can hardly be called "illiterate"), but instead explains the frequency of its occurrence.

George O. Curme starts his review of Part III:

There is nothing in the domain of philology more stimulating than a new volume by Professor Jespersen. . . . For many years he has been out on the confines of our knowledge fighting to extend its boundaries into the great unknown. The new volume brings us many more valuable contributions.

– whereupon he starts to describe how Jespersen's and his own views on grammar diverge. The pair disagree on the category of here in "leave here" and that of poor in "the poor", on the virtue of replacing the familiar term noun clause with content clause, on whether can, must, shall, etc are verbs, and more. Curme's objection to Jespersen's denial of the existence in Modern English of a dative case is expounded at some length; but simply, the identity of form in "They chose him a wife" to that in "They chose him king" does not deter Curme from saying that the former is an example of the dative. And this is before Curme "turns to what interests him most in Professor Jespersen's new volume – his treatment of relative pronouns".

Part IV. Syntax. Third volume. Time and Tense First published in 1931. The chapters are:

This part also has a long "Abbreviations and list of books". The great majority of the books listed are works (largely of fiction) that Jespersen credits for examples. Thus for instance an example of past tense dare not is attributed to "Caine M 378" (MEG IV:12): this is page 378 of what "Abbreviations and list of books" explains is Hall Caine's The Manxman (London, 1894) (MEG IV:xii).

Curme's review of Part IV starts by commenting on its treatment of expanded (i.e. progressive) tenses, a treatment that he finds of interest, but inadequate. Unlike Jespersen, Curme uses the term aspect as well as tense; he rejects Jespersen's denial that English has no "real future tense".

Part V. Syntax. Fourth volume First published in 1940. The chapters are:

Also included is "Additions to the list of abbreviations in vol. IV".

The preface thanks the Carlsberg Foundation for its continuing support; the prefaces to Parts VI and VII do the same.

Francis states of nexus, a concept important to Jespersen, that it "is nowhere dealt with within the first three Syntax volumes of MEG". In view of the coverage of nexus in the second volume – remarked on in a review – this must be mistaken. But aside from the matter of earlier appearances:

[T]he fourth Syntax volume of MEG . . . is wholly devoted to nexus and contains eleven chapters, nearly 200 pages, on infinitives. This is one of the most complex areas of English grammar, and remains one of Jespersen's most distinguished accomplishments as a grammarian.

In a review of Parts V and VI, Simeon Potter determines that "The dependent nexus is the main theme of Part V: a simple nexus as object; a simple nexus as regimen of a preposition; a simple nexus as tertiary; nexus-substantives; the gerund; the infinitive; clauses; an implied nexus (agent-substantives and participles)." He criticizes the book in places, but his praise includes the observation that:

No one has discussed ellipsis, that cardinal problem for the syntactician, with greater ingenuity than Jespersen. Aposiopesis, prosiopesis, suppression, subaudition, sous entendu, latent phrase and incomplete clause have all been illuminated in their turn.

Part VI. Morphology This was first published in 1942.

Jespersen "was content to delegate the major part of the work to [Niels] Haislund and . . . Paul Christophersen and Knud Schibsbye" who had to work with his lecture notes from 1925. Jespersen did carefully examine the result. His preface to Part VI gives more detail, stating which chapter, and often which section of which chapter, was written by which of the four; and, where he himself was one of the writers, then sometimes also when (from 1894 to 1942) he had written it. However:

In consequence of the manuscripts having in some instances passed to and fro between others and myself it would now be difficult for me to decide which particulars are due to me and which to my co-workers. But anyhow the full responsibility for any shortcomings rests with me exclusively. (MEG VI:v)

The circumstances of editorial work on Part VI were not happy:

When writing the first four volumes of my Grammar I was in constant touch with friends in England, most of them competent scholars, whom I was able to consult on knotty points. If it had been possible I should very often have done the same with regard to this volume, but to my great regret the unfortunate happenings to my country during this miserable war have prevented me from asking the advice of native Englishmen. A few pages, however, were revised by the then lecturer in the University of Copenhagen, Mr. A. F. Colburn, before he was forced to leave Denmark. Something is rotten in the state of the world. May Heaven direct it! (MEG VI:vi)

"This volume naturally falls into five parts", writes Jespersen, describing these (MEG VI:5):

The chapters are:

In the context of the "naked word" – as seen in "My back hurts", "He's back", "I posted it back", "You should back out" – Jespersen claims that:

The development of such identical forms must be reckoned one of the chief merits of the language, for this "noiseless" machinery facilitates the acquirement and use of the language enormously and outweighs many times the extremely few instances in practical life in which ambiguity can arise. . . . Anyhow it is ridiculous to say, as is sometimes done, that English no longer distinguishes between the parts of speech, between noun and [verb], etc. (MEG VI:85)

While conceding that Part VI and Herbert Koziol's Handbuch der englischen Wortbildungslehre (1937) "admirably supplement each other and both are equally welcome", Simeon Potter finds that the former "contains numerous errors and perpetuates many incomplete statements of historical fact". He provides a great number of these and says that constraints on space preclude the provision of more.