In the sequence of musical epochs, this sub-genre follows the development of opera and of the so-called opera seria, which should have been perhaps a constrasting sub-genre due to some of its formal and ideological characteristics. Opera was however turning the seriously celebrated classic music into something more "readable" by musicians and listeners. The reason for the great success of opera in general, has been in this sort of "descent" to more popular and understandable themes, together with the contemporary approaching to theatre (of universal comprehension, over an average moderated cultural requirement of the spectator).
In this climate, opera buffa was one among the many forms in which the evolution of music contacted the audience with more friendly "manners": the French Opéra Comique, or the German Singspiel, as well as the German Melodram (very similar to the French Mélodrame, but not related to the Italian Melodramma). These were all sub-genres in which the recitative (the spoken, and not sung, part of the work) started to increase its presence within the body of related works, while the "purely" musical part was proportionally decreased. Music and talk (recitative, which in reality is recited over an essentially basic music, sometimes of chamberistic echoes) started then to experience an interesting symbiosis which the public seemed to enjoy. However, some of these evolutions were not going to completely abandon a formalist or emphatic state of mind, as happened for the French déclamation chantée, that soon re-joined the tragédie-lyrique of Jean-Baptiste Lully and was re-absorbed in more traditional measures.
Popularity was the writers intention, so these "experiments" (as they were called by resisting formalist musicians) also had intelligible vocal contents. This is in contrast with a traditional music that, after Gregorian Chant, had passed to rigid formal schemes extended in Latin or in German, never comprehensible for the general public. Abandoning these languages for the more friendly Italian and French, Recitativo instead broke that habit (which also rendered music an exclusive interest for certain cultural communities, and not even all of them). The public was finally able to decipher the words that singers pronounced, the story beyond the music was intelligible. It was a relevant movement toward laical themes "de-sacralised" music, allowing acceptance of a concept of "music for mere entertainment".
Most of these facts regard opera in general, but Opera buffa in particular. It is indeed very difficult to adopt a formalist scheme for a classification of Opera buffa, since no one would ever deny the serious content and value of some among the best known works that are usually ascribed to its kind, even when they declaratively are a "Dramma giocoso" rather than expressedly an "Opera buffa", and we generally include them all in "Opera". Any distinctive element has therefore to be considered in a relative proportion, in comparison with the many singularities that each work showed.
Certainly, while Opera seria dealt with mythical subjects such as gods and ancient heroes, and only episodically contained comic scenes, Opera buffa had those scenes as its most important part, and sometimes the reason for the opera itself. Music was going in the direction of public, so what could be more appropriated than themes and stories that common people could have enjoyed? Comic stories in opera were the final translation (for the times) of music for entertainment.
In some of the Opere buffa, a language was used that the lower class would relate to, often in the local dialect, and used caricatures that were often found in Italian commedia dell'arte.
It is sometimes affirmed that in Opera buffa musical content is often simpler, maybe poorer, limited in length and in fantasy, and these would be sufficient reasons not to include it in the higher genres. Nevertheless, the (now) not discussed genius of Mozart didn't miss the chance of giving us a masterpiece (Le nozze di Figaro - in Italian), or perhaps two (with Don Giovanni) and was followed by pretty all the major composers. And it must not be forgotten that instruments and voices were developed within this musical area and later accepted for other compositions too, as the Puccini's basso buffo in Tosca (the Sacristan).
Obviously the role of the libretto writer became fundamental. It has been noted that while music was "popularising", librettos still used a language that remained far from the one commonly used (even if it was no longer Latin or German), and in some case what music had gained in simplicity, text had lost by preserving emphasis. The operistic composers that meant to finally be comprehensible with an entertaining music, found in Librettisti their "croce e delizia", their torture and delight. Librettos became the conservative part of Opera, and were the element of opera most contested by the public who often could not follow the content or, eventually, could misunderstand it. A famous emblematic case is in Verdi's Il Trovatore, where the verse of the Count: "Ah! l'amor, l'amore ond'ardo" (Ah, love, the love I'm burning of) was by assonance generally received as the more probable "Ah! l'amor, l'amore é un dardo" (Ah, love, love is an arrow) (an example of a mondegreen), and this only because the general style of language used would not allow a complete understanding by ear (without the written text to read), and because the general phraseologic sense of the duet was not simple. But rhyme reasons and poetical licenses were invoked by librettisti, frequently doubtfully discharged.
The type of comedy could vary, and the range was great: from Rossini's The Barber of Seville in 1816 which was purely comedic, to Mozart's The Marriage of Figaro in 1786 which added drama and pathos. The genre declined in the 19th century, and it is often considered that Verdi's Falstaff, in 1893 was the last of the Opera buffa.
Some authors have advanced the idea that one of the important aspects of Opera buffa would be that it imposed the attention on the audience, rather than "on conservatories", and this helped the greater Opera too to milden its melodies in order to be more easily and widely accepted. Also, it is said that Opera buffa was a sort of demonstration of the concrete possibility of breaking rigid rules, yet consolidated, that before were considered unchangeable. Moreover, some critics usually recall the famous insertions of popular themes (i.e. choruses and voices in Bizet's Carmen, as well as the tarantella in Tchaijkovskij's all-musical Capriccio Italiano) as different examples on different fields of the constant need for musicians to get out of formalism, to let everyday life enter music, after the essential lesson of Opera buffa.
On an external side, French Encyclopédistes considered Opera buffa "à l'Italienne" a positive response to the imperative schemes then used, and made it become a sort of symbol of compositive freedom.