On the surface, Rodrigo's songs are composed of lyrical melodies that paint a somewhat aesthetically pleasing picture of whatever image the listener chooses to associate with 'all things Spanish'. One must, however, have an understanding of the tradition from which Rodrigo was drawing his material in order to understand the importance of his work.
The history of the art song in Spain has been one of anything but continuous development since the 16th century. This "Siglo de Oro" in both the music and the theatre has been called by some the "Great age of Spanish Song"(1). Composers combined the rich poetry of the age with a lyrical melody, usually accompanied by vihuela, as a new means of communication both between individuals and at court. Polyphony took over in the 17th century, which eventually gave rise to the zarzuela, a form of opera with spoken dialogue, dances, and ballet accompanied by castanets and guitar. Italian influence gave rise to the tonadilla, creating a kind of "guerre des bouffons" conflict between this new form and the more traditional zarzuela. As the Italian style grew in popularity in Europe, so did the tonadilla in Spain, establishing a new Spanish idiom that included iambic concluding notes to phrases and cadences, a melodic structure that used intervallic improvisations on a chordal framework, and ornamentation that tended to create triplets in the melody(2).
Granados renewed the tradition of the tonadilla in the 19th century, while attempts to revive the zarzuela ('zarzuela moderna') were only mildly successful outside of the popular tradition. It was Manuel de Falla who brought back an appreciation for the origins of Spanish song by combining the impressionism of friends Debussy and Ravel with the folk music of the Golden Age(3). This resulted in new settings of folk-songs with "brilliantly pianistic" accompaniments(4).
Following in the footsteps of his close friend de Falla, Rodrigo too developed a desire to go back to the "roots" of Spanish art song and create a new repertoire based on these melodies. In the aftermath of a civil war lead by a powerful dictator, the time couldn't have been more appropriate for Spain to unite itself through music by means of Rodrigo's neo-classicism. Rodrigo's songs revive this tradition while simultaneously integrating elements of the tonadilla idiom of the 18th century, creating a new form that serves as a kind of link between past and present. Consider as examples the ornamental triplet "grace notes" of "Cancion de cuna" or the lively broken-chord melody of "De donde venis, amore?" from "Cuatro madrigales amatorios". More important to Rodrigo, however, seems to be his appreciation of the literature of the 16th century, employing texts from playwrights and poets such as Unamuno and Lope de Vega. In this way, his music reflects the more integrated and, some may say elevated, art song of the Golden Age.
Another interesting fact that seems to confuse Rodrigo's critics is that, the composer's nationalism not only unites the past with the present, but the popular tradition with art music. Those that choose to dismiss Rodrigo's songs as merely tuneful melodies without any innovative intellectual substance may, in fact, be recognizing and rejecting the use of popular idioms in his music.
(1) Stevens, p.382
(2) Stevens, p. 388
(3) Spanish song companion, p. 106
(4) J.B. Trend, as quoted in Stevens, p. 391