Classic Rag

Classic rag (short for classical ragtime) is the style of ragtime composition pioneered by Scott Joplin and the Missouri school of ragtime composers. These compositions were first considered "classic" by Joplin's publisher, John Stark, as a way to distinguish them from what he considered the "common" rags of other publishers. Today, any composition fitting this particular ragtime structural form is considered classic rag.

In the earliest days of ragtime, there was little consensus on how to print the syncopated melodies of ragtime, so there was considerable variety in the formatting of sheet music. Pieces appeared in common meter, in 4/4 time, and in 2/4 time, and often followed conventions of earlier musical forms such as the march. As the 20th century dawned most composers, arrangers, and publishers began to settle on a common set of notational and structural conventions, and because Scott Joplin was the best-selling ragtime composer in that era, his conventions eventually predominated. The "classic rag" form can thus be considered a typical form of a ragtime piano composition, though it is by no means the only form.

In idealized form, the classic rag has the following structure:

This can be written more succinctly as: INTRO AA BB A CC DD.

Few classic rags follow this idealized form, which is only a generalization; there are a number of standard variations:

In the later years of ragtime, under the influence of Tin Pan Alley, a shorter three-strain form (omitting the D strain) became common.

Rag strains themselves have considerable structure. The treble clef (played by the right hand) typically contains the syncopated melodic theme, while the bass clef (the left-hand part) grounds this theme rhythmically with a regular, alternating pattern of eighth-notes (a walking bass).

The sixteen-bar strain is often structurally divided into 4 four-bar phrases, the third phrase repeating the first. There is considerable variation, though. Some composers (such as James Scott) made frequent use of two-bar phrases and others (such as Joseph Lamb) tended to employ eight-bar phrases.

...
Wikipedia