Though they never met, as far as history has recorded, Vivaldi and Bach are tied together as much as any two great composers. The basis for this connection is the fact that Bach transcribed some of Vivaldi's concertos in his early career for keyboard (either harpsichord, organ, or in one case four harpsichords and string orchestra). This connection point, along with the popularity and greatness of both composers' music, has lead to constant comparisons.
In some ways, two composers from the same age could not be less suited for comparison. Vivaldi, during his life, was an international figure, while Bach remained a provincial composer. Bach arranged Vivaldi's works like a student might to learn from great Italian music, yet his greater reputation in later ages has reversed this role: Some see his transcriptions of Vivaldi as improvements, or at least as another chapter of evidence touting Bach's superiority. Vivaldi was from Italy, and in their times the Italian style was the leading international style. It was considered the most modern, the setter of trends and the most desirable approach. Later, scholars and musicians of Classical music would look back on this with doubt---many saw the Northern styles, particularly those in what is now Germany as superior in a modern and 'ideally Baroque' sense. The national tastes were different. Germany had more complex part writing, with a thicker sound. They used woodwinds more often, and with more freedom than the Italians and the practice of orchestral winds and brass took root there. In Italy streamlined simplicity was valued. Clarity and directness were the basis for musical vocabulary. Formal innovations such as the invention of now staple genres like the solo concerto, the orchestral concerto (which would develop into the symphony) and da capo aria began there. At the time, the Northerners looked down on their own strengths often, and it was common for patrons to bring in Italian talent (on up to Mozart's day). This was not much of a two way street. Italians coming into Germany were rarely influenced by the thick part writing or counterputal footholds. Vivaldi, for instance, wrote for the Dresden court at times in his career. His style was little effected by his travels, though. The main German influence was allowing him to write for orchestras with more woodwind players and the adjustment seems to have been a natural and happy one. For what it is worth, Bach absorbed a variety of formal and stylistic cues from the Italians (which he was openly fond of) without giving an inch to his own personal style and tendencies.
Perhaps a good way to start comparing two tough comparisons is to speak in terms of 'national' styles. To be a bit overly simple, Bach was greatest exponent of the German style and Vivaldi was the greatest exponent of the Italian style. In a way they were polar about it---Vivaldi takes the values of the Italians to an extreme---he was wildly inventive, trail blazed forms, wrote emotive music, and valued boldness and clarity. Bach also takes the 'old-fashioned' stereotype of Germany at the time to an extreme. While his music is timeless and modern in many ways, even his fellow Germans saw him as unusually out of date. Perhaps a better way to put it is that Bach valued things that were no longer fashionable while most of his fellow countrymen (Telemann is a great example) were going to great lengths to absorb or even imitate the Italian approach.
In this simple context, Vivaldi and Bach were Baroque opposites. Bach obsessed over complex part writing, full of motivic variation, and references between parts. It is rare for counterpoint to not at least influence the way Bach creates a passage. Variation and counterpoint and references of these two ideals show up everywhere in Bach's music. To Bach, music was an intellectual pursuit and the evidence of God that resided for him in music was strongest when his works were full of rich references and clever working out of material.
Vivaldi was actually quite adept at counterpoint and the kind of motivic working that Bach used, but he did not value it in the same way Bach did. For him it was just another musical tool, one to be used rarely at that. Vivaldi did not work out an intellectual score as Bach did. He was concerned with how a work sounded, and with expressing vivid emotions. Textures and shapes were the tools of Vivaldi---not texture in the music theory sense of homophony, monophony and polyphony, but in the general artistic sense. His music strives to convey different textures of aural surfaces. To Vivaldi, music was emotional and artistic and the evidence of God that resided for him in music was strongest when his works stirred the emotions of his fellow men.
For two so totally different musicians, there might seem to be little common ground, but they actually share many characteristics. Perhaps the most obvious is that they both write in a style that is instantly recognizable. One gets the feeling that, even though they had no interest in hiding their artistic identity, neither would be able to keep their strong musical identities under wraps even if they tired. Bach, in particular would often get caught up in the experience of composing, and the result would be longer and larger scale pieces than were generally written at the time. Both men had a formal knack which put their contemporaries to shame. Vivaldi's formal conception of the concerto in the first fifteen years of the 1700's was far ahead of any of his contemporaries. He also had a modern, striking musical language that was head and shoulders above his fellow Italians at this time, and the mix of the two made his music internationally renowned. While Bach can't claim to be quite the creator and nurturer of forms that Vivaldi was, he always looked at formal aspects of music in a way beyond what his fellow men were intellectually capable of. This allowed him to write at a top level in any form he chose and to add small additions of his own to forms that would later be admired and noticed. He also did make smaller contributions to form in the way Vivaldi did with the concerto. Bach was one of the first to compose sonatas for solo instrument and keyboard that were not solo/accompaniment so much as an even pairing between a 'melody' instrument and a keyboard instrument. This format fit his style and nature well.
Striking little similarities also occur. Both men were fond of passages that are rhythmically repetitive, embedded in more varied material, in which harmonic progression was the main interest, and which create a hypnotic effect. This device which is hard to describe, but instantly recognizable was used constantly by both. Bach certainly took the idea of orchestral unison (examples come from Brandenburg Concertos #3 and 2) from Vivaldi. Bach may also have taken from Vivaldi the idea of inserting cantabile material into a fast movement. Vivaldi's striking and elaborate use of this concept in the 3rd movement from his opus 3 no. 8 concerto is perhaps the first appearance of the idea in music history. Bach's use of this device in the 3rd movement of his 5th Brandenburg Concerto may be a direct reference to Vivaldi's opus 3 no. 8 (although it lacks Vivaldi's melodic luster). Both passages are marked cantabile in the score.
Another similarity is that during their lives, both men had perhaps acquired greatest fame for their mastery of their home instruments. Bach was best loved by his contemporaries as an incomparable organist. His improvisations were talked of far and wide. Vivaldi became internationally known as a composer, but his most profuse fame may have come from his violin playing. As early as 1712 he was playing in positions beyond the fingerboard of almost any contemporary violin.
Perhaps a good way to look at these composers is through the 'interaction' that connected to them, and the perceptions that have developed as a result. One becomes instantly impressed by Bach's open mind and humility when one looks at the Vivaldi (and other Italian) transcriptions. Clearly, he never intended to write music that would be like their's, but he sought to learn everything he could from them and use what he valued in their approach. This sort of humility and attention would be commendable in a run of the mill student, but in a man with the massive abilities of Bach, it seems like a small miracle. On the other hand, Bach seems to have missed the point at times with the transcriptions. They are not literal, and he often takes liberties to 'Bach them up'. This most often means filling out the parts with small canons, references, or rapid bass passages to fill out the texture. Often this process dispenses with the strengths of the original---boldness, clarity and emotional directness. Bach may have seen these changes as required by the switch of instrumentation---from string orchestra to either organ or harpsichord. Adding to the challenge is early Vivaldi's almost schizophrenic range of approaches. Two of the pieces Bach arranged could hardly take more varied approaches. Vivaldi writes a fugue in his opus 3 no. 11 that is one of the few works to come out of Italy in Bach's counterpuntal realm. On the other hand his opus 3 no.12 is, orchestrally, limited to simple three part writing (often only 2 real parts) in the first movement. Ironically, the less Bachian work (no. 12) seems to come off better---it has it's own charm as a piece that makes both compositions viable. The grand Organ transcription of opus 3 no. 11 is enjoyable, but dead sounding when compared to the original. Vivaldi's counterpoint is so good in it that Bach made very few additions or changes. The non-counterputal sections seem muddy compared to the original. Perhaps Bach's greatest sin in the transcriptions is his version of Vivaldi's opus 7 no. 11 (Il Grosso Mogul), which he transcribed for organ. This work is unapologetically violinistic. Any transcription to keyboard would be risky, because Vivaldi's version relies on the expressive touch available to violin articulation (and not available to mechanical keyboard instruments, for all intents and purposes). But Bach's choice of organ, with it's muddy articulation, makes the work hard to bear.
But a failure of this type is often written off as being a defect in Vivaldi exposed, by modern audiences. The idea that Bach was 'improving' the works may be an offshoot of these modern attitudes. Though Bach's versions are more Northern sounding, it could be argued that most of his changes are to make the crossing of mediums bearable. Knowing Bach's own musical personality---at once a man of unimaginable discipline, yet one to give in to his hunches or get swept away by the act of composing easily---I can read many moments in his transcriptions where he simply could not resist putting in his own idea or reworking something in his own way. And this brings up an important difference between the two men. Logically, one would expect the emotive Vivaldi to be less disciplined than the intellectual Bach. In many ways Bach was as disciplined as any composer in history. But he also got swept up in process in a way that was more romantic or modern than Baroque. He could not resist a good idea if it came to him. This has the effect of pushing his luck with the attention span of the audience. Perhaps no composer who ever lived could work extremely simple ideas with clever variation the way Bach could—working the material. And that is the approach he preferred. He would set simple ideas up and build off and vary those. With this way of working Bach has wowed countless people, yet his approach has its limits, even for perhaps history's greatest composer. Bach often squeezes every drop he can out of a small amount of initial material. He enjoys this process, and perhaps its challenge, and it gives his works total unity within a movement. But his lack of new material and how long he is willing to (cleverly) stretch the material, sometimes into ten minute movements, based on the same material and employing mostly thick textures, can weary a listener, whether people admit it or not. In this way he demands a lot from his audience.
Vivaldi, on the other hand, was careful to not push the listener in such ways. He is careful to introduce new material when needed, vary the texture (this is perhaps why he enjoyed the concerto so much) and never have a piece last longer that the material could support. While some might accuse Vivaldi of lacking ambition at times, he simply wrote with a fear of overextending the material, and the audience's patience. Audience psychology was always on his mind. One sometimes gets the feeling that Vivaldi cut things off when he still had valuable ideas because he felt he was pushing a work past certain ideals he had in his head about audience psychology. Vivaldi is never afraid to appear banal at first glance---he knew he'd win over listeners in time. He also wrote music of consistent quality, but was willing to compose some pieces to be miniature and light, lacking huge demands, and seeking quick charm. Some concertos for string orchestra (without soloist) by him run a total well under five minutes. On the other hand he wrote concertos with soloist that ran beyond sixteen minutes.
Momentum was important to both men. Both use sequences often. Vivaldi's tend to be longer and less camouflaged with part writing detail. Bach's heavier parts tended to muddy his momentum, so he gained more kinetic energy from passing material around the parts and having a restless energy resulting from rapid passage work in all parts. But the rhythmic drive and pure forward push of the music of Vivaldi is unequaled. This points to another difference from a similarity---Vivaldi is perhaps the composer of the greatest rhythmic vitality of all time, while Bach is perhaps the most harmonically thorough and perfect composer of all time. In this respect Vivaldi and Bach are mirror images of each other. Vivaldi's rhythmic vitality is made possible by a surprisingly advanced sense of harmony, although his effects are often achieved with simplified harmonic tools. Bach's harmonic variety and mastery is put into relief by his strong sense of rhythm. He is always careful to set up his basic material to be full of Vivaldian rhythmic vitality of a sort.
Perhaps what sets Bach apart from all other composers is his adventurous yet logical harmony. No other composer could get to the harmonic places Bach travels without leaving logic behind. For Bach it is almost as natural as breathing. In this respect Bach has been wowing people for hundreds of years. It is an obvious technical prowess he can hold over every other composer in history. It makes people claim he's the greatest composer of all time, and it makes it hard to logically argue against such assertions. Vivaldi, in contrast, has no counter that is so obvious. He's a great melodist, has a great sense of harmony, great rhythm and a great sense of form. But in none of these single aspects can he do things that no other man has been able to. For Vivaldi, it is about what you get when you put all those tools together in the hands of a man with a great gift for communicating pathos and a sense of creative adventure rarely seen in music. While Bach's harmony can be a measure of all other composers', it is his over all product and how it stands above his contemporaries that has passed his music on to us in a timeless manner. Vivaldi is similar. No other composer has combined the gifts that he had with the almost frightening urge to create. His quality is likewise head and shoulders above his contemporaries. He was an innovator, in form and in musical language. He was on the basement floor of the creation of the concerto. Perhaps the concerto would not have caught on enough to stick as long as it has without Vivaldi. Yet, though he was one of the first composers to write concertos and in the ritornello form, he adapted and evolved subsequent approaches so that his music was as up to date and ambitious as contemporaries of two generations below him. While Bach was a steady island, whose quality was naturally invariable, Vivaldi proved over and over he could match any young composer coming up.
Both Vivaldi and Bach were very prolific composers. Vivaldi is often chastised for being too prolific, as though he did not take care when writing. Numerous corrections in his scores suggest otherwise. Bach is simply a slight variation of this---he is very prolific to, but in a different way. Both men were compulsive composers. Vivaldi comes from the Mozart school of composing, in that his mind worked faster than he could dictate. Inspiration flowed like a gushing spring, and composing was more a matter of capturing that energy and putting it in the context of proper forms. Bach's prolificy comes from hard work, immense competence, and playing or working with a limited amount of initial material. He tinkered with his scores, bending and shaping the original material to suit the larger piece, and pulled the material through a full harmonic journey. This might sound like a slower means of composing, but for Bach it was a simple formula in which he could write any piece and make it fresh and original. A man with Bach's particular gifts could compose in this manner at a very quick rate. Both composers lived in an era where massive prolificy was expected. And neither had any problem with such cultural demands. Strange as it may seem, the culture they lived in asked for this much music because the apatite for new music was very large. People did not devote time to preforming past composers. The result of this was a throwaway consumer-like culture when it came to music. Vivaldi and Bach were expected to provide many compositions where they worked. They may have been philosophically uncomfortable with this culture, but they were able to work well in it. Both men kept an archive of old works and reworked them later for different purposes. This may have been due to pressure to come up with music fast, but it may have also been a form of reflection over past compositions, almost out of nostalgia or at least fondness. So perhaps to the composers themselves, music was not so easily disposed of. But most of the music was written for one performance, a short period of performances or at best a work that an amateur patron would plan to play until he mastered it and wanted to try something new. After this, the works collected dust unless the rare instance of reuse by the composers came up. This culture is at odds with the sheer quality of both composers' music. From an audience psychology perspective, it is easy to listen to most of Vivaldi's and Bach's works many times without being bored or restless. This freshness, oddly, is sometimes less apparent in the music of later periods, even though this throwaway music culture began to subside.
But what tries one person's patience may be a rich experience for the next person. And that fundamental difference of experience is alive in both listeners' minds and Vivaldi and Bach's different approaches. For Bach, music was an ideal and a craft. It was an idea of intellectual perfection, a balance of various elements of music all held to lofty structural standards. Music, to Bach, needs to look good and full-bodied when written down. How the music sounds is important to him, but perhaps secondary to meeting a standard of construction forged from density and working clever, seemingly limitless ideas out of the simplest building blocks. Bach strove to construct something beautiful with his music, with the resources at hand---as much a beautiful idea as beautiful sound. He was a craftsman and approached his music in a practical manner, where logic always dictated the role of his emotion and creativity. He built with the most modest tools, focusing on quality and structural integrity. His harmony is immaculate and thorough. He almost looked at it as wasteful to move on to new material or ideas if he had not yet worked out every variant that was worthy from the original motifs. While not ignoring emotion, large structure, instrumentation, orchestration, and genre, his main focus in every piece he approached was harmony and dense integration of the musical ideas. It was about constructing something beautiful, almost solid, like architecture of sound and mind.
Vivaldi was not interested in an intellectual ideal, although structure was important to him. His music, first an foremost was about sound, aural appeal and textures. Through sound and momentum, created with rhythmic vitality and constant sequential variation, he intended to take the listener on a journey. There is a sense of movement, of travel in his music. Vivaldi also wanted to convey emotion directly through music. While much emotion lies in Bach's music, there is not the obvious range of moods, from tempest to tender, from joy to depression in his music. The emotions of Bach must be patiently unlocked, and when they are revealed, they are deep and subtle, but without the extreme relief which Vivaldi's emotional world stands in. In a way, Bach's texture can become overwhelming--- in the big picture very consistently dense. Vivaldi, has a lighter overall texture, but with much attention to variations in texture of all kinds. His music becomes a display for a variety of musical surfaces. This approach not only does not require Bach-like thickness, it requires a thinner, more malleable textural average. It also requires some 'breathing room' in the score to offer musicians the chance to add their own ideas and improvisations. Within this world of scene painting and textures, Vivaldi also has bursts of melody. His slow movements are full of lyricism and melody, but this leaks into the fast movements at times. People overlook this fact, because Vivaldi had other resources he focused on, rather than relying on constant pure melody, as later composers tended to. Vivaldi will surprise the listener with a memorable tune out of nowhere, and he is constantly using catchy melodic cells to construct his music. An example of a melody bursting fourth out of his music is the already discussed cantabile melody from the third movement of opus 3 no. 8. Of this, the musicologist Alfred Einstein had this remark: “It is as if the windows and doors of a stately baroque hall had been opened to welcome in Nature's freedom: a superb pathetic grandeur such as the seventeenth century had not know; a cosmopolitan's cry to the world. It is worth remembering that such must have been known to Bach, and that he, wrapped up in himself, never ventured into this open country.”