This work can be seen as the third and final volume of a trilogy, the first two parts of which are Adams's Bilingualism and the Latin Language (2003) and The Regional Diversification of Latin 200 BC–400 AD (2007). These three volumes have changed the way in which the Latin language and its development into Romance is studied and conceptualized, and will set the research agenda on Latin for decades to come. No less than in his previous works, A.’s unsurpassed knowledge of the Latin language and his outstanding philological acumen is everywhere on display in this book, which contains a wealth of new insights into Latin texts of all periods.

Readers familiar with Bilingualism and Regional Diversification might expect this book to be organized along similar lines, with sections devoted to the language of different social classes at various moments of Roman history. However, anyone hoping to find an account of, for example, Plautus’ depiction of the language of slaves or a discussion of the language of Roman equites in the late Republic will be initially disappointed, since the book is structured as an examination of specific linguistic features. After a relatively brief introduction, thirty-two chapters systematically assess whether developments such as the dropping of final consonants or use of prepositions in place of bare case forms are necessarily indicative of the social background of the speaker or writer. The bulk of the book is taken up with consideration of phonological and morphological or morpho-syntactic matters (including the development of the article and reflexive verbs). There are briefer treatments of aspects of subordination and word-order; a short chapter on Latin words for body-parts stands in for an extensive study on the lexicon (which is beyond the scope of an already large book). The cumulative effect of these explorations is to turn on its head much of the current thinking on Vulgar Latin and the Romance languages.

In order to set A.’s findings in context, it helps to give a synopsis of the development of Latin into the Romance languages as it is often presented in handbooks and grammars. Classical Latin is viewed as the written form of Latin taught at school and employed by members of the Roman élite, and the register in which nearly all literary texts and official inscriptions are composed. Vulgar Latin, on the other hand, is presumed to be the spoken idiom of the lower classes, represented in writing only rarely and imperfectly. (A. gives a handy survey of some of the different senses given to the term Vulgar Latin in modern scholarship at 7–27). Vulgar Latin has been held to be the ancestor of the Romance languages, and consequently it has been assumed that anything which looks like a Romance feature in surviving Latin texts is necessarily a vulgarism, and indicative of a lower-class origin. A. shows that this picture is far too simple: features which prefigure Romance developments do not all reflect the Latin of the lower classes, but sometimes stem from the Latin of the élite. A.’s discussion of the Latin verb eo ‘I go’ in ch. XXXI (792–820) can be taken as an example of his approach and findings. In the modern Romance languages the shorter forms, such as second and third person is and it, do not survive. Hence French je vais, tu vas, il/elle va ‘I go’ etc. are all derived from a different Latin verb, uado. But the stem i- survives in the French future, j'irai, which ultimately descends from ire habeo ‘I have to go’. Many scholars have thought that the avoidance of the short forms of eo and their replacement by uado in ancient texts were indicators of Vulgar Latin, and might indicate a lower-class origin of the author. But A. makes it clear that this is not the case. Writers of literary prose avoid the short forms already in the late Republic, and uado entered the language originally as a high literary synonym for eo before gradually permeating through to lower registers. The Romance form in this case does not stem from the speech of illiterate farm-hands, but from the diction of the élite.

A parallel case is found in the history of the future made from a periphrasis of infinitive with habeo (the ultimate origin of French j'irai ‘I will go’ cited above). The infinitive with habeo construction does not appear with future meaning in texts normally considered to be low register Latin, such as the speeches of the freedmen in Petronius, the private letters of Claudius Terentianus or veterinary texts. But it does appear in the third-century grammarian Sacerdos, and in other grammatical texts, and A. reckons that the construction ‘seems to have had some currency among the educated’ (657), and this is therefore another linguistic feature that has its origins in the language of those with higher rather than lower social status. In other cases too, A. repeatedly demonstrates how constructions sometimes thought of as ‘vulgar’ are much more widespread in literary texts than has been previously thought. For example, Livy shows a preference for ab Roma ‘from Rome’ (fifty-four examples) rather than the bare ablative Roma (which never occurs) with verbs of motion (xvi and 260).

With the demolition of the view that everything in Romance comes from the lower registers, other notions must also be abandoned, such as the idea that the comedies of Plautus preserve a spoken register which goes ‘underground’ to emerge in Romance centuries later. A. does, however, make a strong case for a ‘submerged’ Latin, that is words or expressions which are usually avoided in written texts of all registers in the ancient world, but which must have been widespread in speech in order to explain their ubiquity in Romance and their occasional appearance in sub-literary or other documents. These words include Germanic loanwords such as hanca ‘hip’ (788) or baro ‘man’ (not mentioned in this work but discussed at Regional Diversification, 599–600). None of these submerged Latin words can be convincingly linked to Plautine usages, and many are demonstrably later imports into Latin (as is the case with the Germanic loanwords hanca and baro). Some of this vocabulary does appear to be connected with lower-class usages, but since constructions such as the infinitive with habeo future are also largely absent from our texts, it is important to keep in mind the warning of A. (858): ‘“Submerged” does not necessarily mean “vulgar”.’

Taken together, the chapters in this book therefore present a new picture of the history of Latin. The notion that all change in Latin is ‘from below’ is successfully exploded, as is the lazy use of the term ‘vulgar’ to refer to a social dialect of Latin, the ancestor of the Romance languages and forms which are stigmatized or avoided in literary texts. A. is keen to keep the term Vulgar Latin in play (8–11) but outside of the first chapter it hardly recurs in the main text of the book, and there is a case for saying that the term is now so confused and weighed down with baggage that it would have been better to leave it out altogether.

There will be a temptation for Latin scholars to buy this book and use it as a work of reference. The organization of the chapters, the level of detail and the excellent indices mean that it could profitably service as such. Indeed, reading through the whole thing from cover to cover is a lengthy and demanding task. But the sum is greater than its parts, and those who read through the 900 or so pages will undoubtedly be richly rewarded.