Haydn, having worked for over a decade as the music director for a prince, had far more resources and scope for composing than most other composers. His position also gave him the ability to shape the forces that would play his music, as he could select skilled musicians. This opportunity was not wasted, as Haydn, beginning quite early on his career, sought to press forward the technique of building and developing ideas in his music. His next important breakthrough was in the Opus 33 string quartets (1781), in which the melodic and the harmonic roles segue among the instruments: it is often momentarily unclear what is melody and what is harmony. This changes the way the ensemble works its way between dramatic moments of transition and climactic sections: the music flows smoothly and without obvious interruption. He then took this integrated style and began applying it to orchestral and vocal music.