Manzoni is regarded as the italian writer who gave the decisive contribution for the foundation of the linguistic unity of Italy.
After the barbarian invasions, that contributed to collapse the Western Roman Empire, Italy was divided in small statelets, and over the centuries was invaded by the Germans, French, Spanish, Austrians and so on. Every italian statelet had a separate jurisdiction and developed its own customs, traditions and…language.
From a linguistic point of view, you can well say that Italy in the 19th century, when Manzoni lived, was a conglomerate of dialects, ofter very dissimilar from each other.
Manzoni started the draft of his novel on 24 April 1821 and completed it on 17 September 1823 . The manuscript is anepigraphic (i.e., untitled) and the title of the first draft, “Fermo e Lucia”, is taken from a note written on April 3, 1822 by Ermes Visconti to Gaetano Cattaneo. This first draft of the novel is conserved at the Biblioteca Nazionale Braidense of Milan.
However, already in the first draft you read the expression “gli sposi promessi” which maybe was the title Manzoni had thought of, and it was the title of the second draft which is conserved at the Biblioteca Nazionale Braidense of Milan.
At that time, Manzoni had not effectively dealt with the national language issue: this version of the book (that remained unpublished until 1915, when was published by Giuseppe Lesca with the title Gli sposi promessi ) was a mixture of literary language, dialects, latinisms and even foreign languages.
In a letter of 3 November 1821 to Claude Fauriel, Manzoni observed:
“Quando un francese cerca di esprimere, com’egli può meglio, le sue idee, vedere un po’ quanta abbondanza e varietà di modi egli trova in quella sua lingua […] Immaginatevi, invece, un italiano, non toscano, che scriva in una lingua la quale egli non ha quasi mai parlato, e che (se pure egli è nato nel paese privilegiato) scrive in una lingua parlata da un picciol numero d’abitanti d’Italia […] manca intieramente a questo povero scrittore [Manzoni si rivolge a sé stesso] il sentimento, per così dire, di comunione col suo lettore, la certezza di maneggiare uno strumento egualmente noto ad entrambi […] Poiché, in tal caso, che cosa significa la parola italiano? Secondo gli uni, quanto si trova registrato nella Crusca, secondo altri quello ch’è compreso in tutta l’Italia o dalle classi colte…“.
(When a french tries to express, at the best he can do, his ideas, you can see how much abundance and variety of modes he finds in that his language […] Imagine, instead, an italian, not tuscan, who writes in a language that he has almost never spoken, and that (even if he was born in the privileged country) writes in a language spoken by a small number of italian inhabitants […] it lacks entirely to this poor writer [Manzoni speaks to himself] the sentiment, so to speak, of communion with his reader, the certainty to manage a tool equally known to both […] Since, in that case, what does it mean the word italian? According to some, what is registered in the Crusca, according to others what is understood in the whole Italy or from the cultered classes…).
Manzoni, evidently unsatisfied with the first work, worked at a revision of the book that was published in 1827 (this version is called the ventisettana, from the year of publication ventisette, 27) with the title I promessi sposi, and the subtitle storia milanese del secolo XVII, scoperta e rifatta da Alessandro Manzoni (milanese history of XVII century, discovered and redone by Alessandro Manzoni). Indeed, Manzoni in the introduction of the book states that he adapted the novel from an anonimous manuscript. Though, according to Giovanni Getto, Manzoni took the novel from the Historia del cavalier perduto by Pace Pasini , scholars generally looked at Manzoni’s statetement as a literary expedient to add more realism to the story .
Manzoni, urged to find a way to clean up his book with a new italian common language (that would contribute to establish the language unification of Italy), eventually came to Florence on 29 August 1827, with all his family (14 people!): his wife Enrichetta Blondel, his mother Giulia Beccaria, his six sons and five housekeepers. He took up residence in the Hotel delle Quattro Nazioni (Hotel of the Four Nations), formerly belonged to the Gianfigliazzi family, now Palazzo Gianfigliazzi-Bonaparte, in Lungarno Corsini, 4.
But, why Florence?
Since the Dolce Stil Novo, the tuscan literary school emerged as a model of stilistic beauty, the most notable exponent being Dante Alighieri. The fortune of the tuscan school consolidated with the works of Francesco Petrarca and Giovanni Boccaccio. Later on, Niccolò Machiavelli, in his Discorso o dialogo intorno alla nostra lingua, stated that the florentine language must be considered as the superior language to be preferred. It is worth noting that all these writers were of florentine origins. With centuries of distinguished literary fortune of the tuscan school, it’s not surprising then, that Manzoni looked at the florentine language as the model to follow. Lacking a florentine vocabulary, he thought that the best option for him would be to study the language directly on site.
During his stay in Florence, Manzoni had the occasion to meet a number of personalities at Gabinetto Viesseux (at that time in Palazzo Buondelmonti), including Giovan Battista Niccolini, Gaetano Cioni, Mario Pieri, Terenzio Mamiani, Giacomo Leopardi, and Pietro Giordani. He was particularly interested in listening to the native florentines speaking, and overall took advantage of the help of Cioni and Niccolini, often consulted for linguistic issues. He became a friend of Cioni, who frequently met at his house in via del Campuccio 64, near via dei Serragli.
In a letter of 17 September 1827 to Tommaso Grossi he used an expression that became famous :
“Ma tu sai come sono occupato: ho settantun lenzuola da risciacquare, e un’acqua come Arno e lavandaie come Cioni e Niccolini, fuor di qui, non le trovo in nessun luogo”
(But you know how much I am busy: I have seventy-one sheets to wash, and a water like that of Arno and laundresses like Cioni and Niccolini, far from here, I don’t find anywhere).
According to Niccolò Tommaseo :
“Si lagnava a ragione il Nostro che i Toscani confondessero con la lingua viva in loro il linguaggio dei testi; e che quand’egli ito nel ventisette in Toscana a lavare, diceva, i suoi panni sudici, rileggendo col Cioni il romanzo, e domandandogli se tale o tale parola si dicesse, il Cioni, che pure d’eleganze viventi ne sapeva più che altri molti, rispondesse: «Si dice; l’ha il Lippi». «Io non domando, – replicava il milanese, – se il Lippi l’abbia scritto, ma se a Firenze si dica»”
(“He rightly complained that Tuscans confused with the living language in them the language of the texts; and when he came in 1827 in Tuscany to wash, as he said, his dirty clothes, reading with Cioni the novel, and asking him if that or that word you’d say, Cioni, even if he knew more than many others about living elegances, replied: «You say it; Lippi has it». «I do not ask, – replied the milanese, – if Lippi wrote that, but if in Florence you say it»”)
Manzoni departed from Florence on 1 October 1827, continuing the long revision of his book, that culminated with the publication of the definitive version in 1840 , titled “I Promessi Sposi“, with illustrations by Francesco Gonin and an appendix (Storia della Colonna Infame) . This version is called the quarantana, from the year of publication quaranta (forty).
In the following years, Manzoni was a firm supporter of the adoption of florentine (not to be confused with a generic tuscan language) as the national language. In 1868, Minister of Education Emilio Broglio appointed a commission to formulate useful proposals to disseminate the use of good language and pronunciation among the people. The commission was divided into two subcommissions: a Florentine one headed by Raffaello Lambruschini, and a Milanese one headed by Alessandro Manzoni. Manzoni wrote the report Dell’unità della lingua e dei mezzi di diffonderla (On the unity of language and the ways of disseminating it) . He wrote:
“Uno poi de’ mezzi più efficaci e d’un effetto più generale, particolarmente nelle nostre circostanze, per propagare una lingua, è, come tutti sanno, un vocabolario. E, secondo i princìpi e i fatti qui esposti, il vocabolario a proposito per l’Italia non potrebbe esser altro che quello del linguaggio fiorentino vivente”
(“One then of the most effective means and of most general effect, particularly in our circumstances, for propagating a language is, as everyone knows, a vocabulary. And, according to the principles and facts set forth here, the vocabulary apropos for Italy could be none other than that of the living Florentine language”).
After the report Manzoni wrote the Appendice alla relazione intorno all’unità della lingua e ai mezzi di diffonderla (Appendix to the report around the unity of language and the means of disseminating it).
The appendix, which expands on the issues addressed in the report, was written in response to a report by Raffaello Lambruschini. In May 1868, a few weeks after the appearance of Manzoni’s report, Lambruschini had published a report, which refuted some principles of Manzoni’s and opposed the adoption of Florentine as the national language, stating instead that an italian language existed . Lambruschini assumed that Manzoni wanted to propose the compilation of a partial vocabulary, limited to the words of the daily use and believed that such a vocabulary could be easily accomplished by selecting only suitable words of existing works. Manzoni disagreed, arguing that a vocabulary should be composed following as the sole criterion that of usage.
“anzi col solo adoprare in senso assoluto i termini di «lingua» e di «vocabolario», s’è inteso veramente di significare un intero vocabolario d’una lingua intera”
(“indeed by merely adopting the terms «language» and «vocabulary» in an absolute sense, it was truly intended to mean an entire vocabulary of an entire language”)
In the same year, Manzoni wrote on the same topic in his Lettera intorno al vocabolario (Letter on the vocabulary) , and was extremely clear that the only way to disseminate a national language would be the redaction of a florentine vocabulary, and that the florentine language had to be the national idiom:
“Carissimo Bonghi, […], voi, da bon amico e da bon complice, avete detto che per fiorentino intendevo fiorentino. E sta bene”
(“Dearest Bonghi, you, as good friend and good partner, said that for florentine I intended florentine. All right”)
The florentine vocabulary, promoted by the Ministry of Education (Nòvo vocabolario della lingua italiana secondo l’uso di Firenze), curated by Manzoni’s son in law Giovanni Battista Giorgini and Broglio, was eventually published between 1870 and 1897 .
 L. Caretti, Manzoni. Ideologia e stile, Torino, Einaudi, 1975.
 A. Manzoni, Fermo e Lucia, a cura di Silvano Salvatore Nigro ed Ermanno Paccagnini, 2ª ed., Milano, Arnoldo Mondadori Editore, 2009.
 Gli sposi promessi per la prima volta pubblicati nella loro integrità di sull’autografo, da Giuseppe Lesca, Napoli, F. Perrella, 1915-1916.
 A. Manzoni, Carteggio, parte seconda (1822-1831), a cura di Giovanni Sforza e Giuseppe Gallavresi, Milano, Hoepli, 1921.
 N. Tommaseo, Colloqui col Manzoni, Firenze, Sansoni 1929.
 A. Manzoni, I promessi sposi; Storia della colonna infame, inedita: storia milanese del secolo XVII scoperta e rifatta da Alessandro Manzoni, Tipografia Guglielmini e Redaelli, 1840.
 A. Manzoni, Dell’unita della lingua e dei mezzi di diffonderla, coi tipi della Perseveranza, Milano, 1868.
 A. Manzoni, Lettera intorno al vocabolario, in Opere Varie, Redaelli dei fratelli Rechiedei, Milano 1870.
 G. B. Giorgini, Emilio Broglio, Novo vocabolario della lingua italiana, Firenze, Cellini, 1870.
 F. Capelvenere, Manzoni a Firenze e la risciacquatura in Arno, Franco Cesati editore 1985.
 G. Getto, Echi di un romanzo barocco nei «Promessi sposi», in Lettere italiane, XII (1960), pp. 141-167.
 Il Manzoni e Vicenza. Il “Cavalier Perduto” del vicentino P. P. e i “Promessi sposi”, in Manzoni, Venezia e il Veneto, a cura di V. Branca – E. Caccia – C. Galimberti, Firenze 1975, pp. 89-124.
 E. N. Girardi, Manzoni e Cervantes, in Manzoni reazionario, Cappelli, Rocca S. Casciano 1966, pp. 87 ss.
 G. Santarelli, La finzione di un manoscritto ritrovato ne “I promessi sposi” del Manzoni e nel “Cicerone” del Passeroni, Aevum 43, Fasc. 3/4 (Maggio-Agosto 1969), pp. 324-327.
 R. Lambruschini, Dell’unità della lingua. A proposito dell’ultimo scritto di A. Manzoni, in “Nuova Antologia”, vol. XII, novembre 1869
 A. Manzoni, I promessi sposi. Storia milanese del secolo XVII scoperta e rifatta da Alessandro Manzoni. Edizione riveduta dall’autore.