In the late 17th and early 18th centuries there were two easily distinguishable national styles of music -- French and Italian. By the middle of the 18th century the distinction, although still a call to arms in the world of opera, had largely ceased to be an issue in instrumental music -- a cooling off considerably hastened by the emergence of German music. The predominant ideal of instrumental music, whether German, English, or Italian, embodied a style described by the French word "galant." Like the term "good taste", "style galant" is a conventionally approved phrase which is nowhere clearly defined but which has a number of connotations. In general it is used to refer to that which is modern, current, in fashion, contemporary, of the latest style, as opposed to the old-fashioned, the outmoded, and the "passé." The term was invented during the reign of Louis XIV, but it was most used in a later age, often called "rococo" after the French style of decoration in architecture and all manner of artifacts, from teapots to hairbrushes, and from candlesticks to fabric design.
The style that is called "rococo" aims to be light, where the earlier style was heavy; asymmetrical as opposed to symmetrical; witty and amusing instead of imposing. Rococo is a style of fantasy -- it is a state of mind that aims to charm. The "style galant" in music aimed to do very much what the rococo was doing in applied art and architecture. Its primary objective was to appeal to the widest audience, and hence music had to be simple and natural for both listener and performer. Polyphony was largely discarded, to the point where accompanying parts were completely subordinated to the principal melodic line.
A number of devices were used to split up a chord of supporting harmony. Alberti bass was one of those devices, named after the composer Domenico Alberti (c.1710-c.1740). This device can be found in the works of Mozart as well as many of the lesser Italian composers.
Imitative counterpoint was abandoned since it was looked upon as a learned or "artificial" device, the consistent use of which anywhere outside the Church showed a deplorable lack of taste. Composers in the new style began to condition their listeners to expect a regularity of phrasing, generally into 2- or 4-bar periods, quite different from the practice of Baroque composers. Not only were the phrases regular, but they tended to be short and separated from each other by rests, and cadential affirmations of key were used frequently, in effect separating the material. Textures were made thinner, even to the point of sacrificing the contrapuntal relationship of the bass with the melodic line, which the Baroque had enjoyed. More and more the bass line acts as a simple harmonic support for the upper parts.
The "style galant" represented, in many ways, a radical change of style. Its deliberate simplification certainly made it popular with the public, and it bred into its listeners very different expectations, upon which Haydn, Mozart, and Beethoven built some of their greatest effects. The prevalence of the "style galant" was also counterbalanced by the development of a mannered style of composition, often referred to as the "empfindsamer stil", or the "Style of Sensibility."