The relationship between melody and form is perhaps the central element to the debate regarding what is "musical" and what is not. To take the idea of melody determining form at its most naïve, one can hypothesize a mode of creation in which a melody is conceived and then other elements of a musical work are added to support the melody. There is ample evidence for this prototype in popular music, in various traditions around the world, and of course in certain styles of the Western tradition. In some ways, the idea that a melody should fit into a form is more of a retrograde notion, as the forms often arose coincidentally from melodic ideas in the first place. However, the idea has certainly had its triumphs. Bach's melodies were clearly conceived to fit into a broader harmonic structure, and the entire classical period of Mozart et al. was based on very firm formal expectations to which material had to fit. In the case of earlier music, whereas something such as a ballade has a poetic stanza form, these were frequently modified, and in something such as a cyclic mass, although the words were a given, the music proceeded in various formal-contrapuntal directions. More conspicuously, early organum was based on an underlying melody, which determined both the rhythmic form and harmonic motion of the entire piece, and then upper parts were added. The same can be said to a lesser degree of the later cantus firmus technique. One can then clearly see the 18th century as central to the idea of putting form before melody, as of course the Romantics went on to develop new old ideas on the formal generation of a large-scale piece from a melody. It can be argued that melody was generally placed first both before and after the 18th century.
One cannot get carried away with this distinction, however, and the above survey is particularly cursory. It is clear that part of what makes a masterpiece is a fundamental simultaneity in conception between various musical elements. It is of course these very masterpieces which can change the priorities of subsequent generations with regard to the hierarchy of musical elements. One can trace something of the interaction between these ideas, and the way subsequent generations reinterpret priorities, by considering the early rise of the Baroque with Monteverdi and others as central figures. In many ways, the roots of the early 17th century were as much in the Renaissance as elsewhere, and of course Monteverdi worked consciously in the older style as well. What made the new style was an emphasis on rhetoric, and its application in music. Monteverdi and his colleagues wanted to find a new liberty for text and emotion, and for them this necessitated a more soloistic formal conception in order to remove constraints from the main melodic line. In other words, we see an adjustment in form in order to remove constraints from melody, in a reaction to the dissonance handling in polyphony of the Palestrina style. The new rhetoric was seen therefore as a loosening of form, and a means by which to allow melody to determine form once again. However, not only did rules of continuo subsequently develop which would go on to constrain melodic motion to fit harmonic implications, but the concept of affetti itself was transformed by its success into a more formulaic idea which no longer involved such capricious melodic inspiration. It should be obvious just how complicated the idea of liberating melody from form can be, and how frequently short-lived the results.
Perhaps it is interesting to note that there have been frequent efforts to allow melody a freer role in determining form, but fewer attempts in the reverse. Ideas to let form actually produce melody are either limited in scope, or very isolated or debatable, such as some postmodern musical techniques. In order to refine and develop this relationship, the rhythmic context of a melody is also important, and indeed frequently difficult to separate from any harmony-conditioning role. Use of syncopation and the resulting displacements in harmony can make the latter remark more than clear. However, the question of whether rhythm is integral to melody is far trickier, as is the relationship between rhythm and form. In some sense the difference between larger scale forms, poetically based phrase structures, and individual rhythmic elements is only one of scale. There is no question but that the height of form constraining melody in the 18th century also produced a contraction of possibilities in phrase structure and rhythm, although it is unclear exactly what this implies. The mostly sensible idea of melody needing a rhythm by definition in Western music is eliminated from general consideration by the completely unmeasured melodic constructions in other traditions, principally the alap preludes within the highly structured raga system of India. What cannot be eliminated from the definition of raga is the grammatical structure of phrasing, and so one can postulate that the supposition of rhythm as an integral melodic factor in Western music is actually a conflation caused by the clear rhythmic patterns which dominated historical poetic forms and therefore phrasing. The more complicated phrase patterns in Indian music expose this distinction, although the same could be said for some medieval repertories, especially the unmeasured troubadour songs and dual rhythmic conceptions of the later Ars Nova. Of course none of these have been central to the formation of the Western concept as it stands today.
The idea of phrasing, or some contextual element, being necessary for the conception of melody is nonetheless critical. It allows us to eliminate an unarticulated and undistinguished series of bare notes from consideration as a melody, and this is reflective of the way music is constructed and perceived. Without a lexical context, an extracted series of notes might be nothing at all. Once one establishes this context, and for some cases the most natural context is of course simply standard harmony, then details of a melody will indeed suggest elements of larger form. For a typical Western musician, it is perhaps easiest to appreciate the converse of this fact. Certain melodic elements, such as non-scale tones or uneven rhythmic values, are simply not conducive to placing a theme into common time harmony. Points of this discussion will be elaborated in the next article, especially as they pertain to modern and fusion efforts.