cont.
'almost all music has a form or structural logic of some sort. indeed, composers provide formal logic in their music so that the listener will better be able to follow the 'course of events.' in this sense at a low-level, form can be likened to punctuation in a language. without punctuation (written down or inflected in speech), in is very difficult to understand the meaning of a text, although the sound of individual words may still have some basic appeal. composers create a form to music by dividing it into structural sections by the principles of statement, repetition, contrast, and variation. the analyst needs to identify those sections - but how? how do you know when the composer has moved from one unit to another?
in vocal music, there is a text, and the logic of the words will sometimes dictate the number and division of musical sections. however, with or without a text a composer provides numerous musical clues to his intent. a change of musical materials is the best clue. if the composition is based on A B A arrangement or form the B section will be set off from the A section by a wide possibility for music changes. for example, the melody of the B section might change (thus B-flat major in the A section and E-flat minor in the B section or simply D major in the A and D minor in the B section); the contrasting section might be placed in 3/4 while the A section is in 2/4 or there may be smaller rhythmic values used in the contrasting section; the B section might include a countermelody which does not appear in either of the flanking A sections; of the A sections might be played by strings with winds added for contrast only in the B section. any or all of these changes (and many others) might be used to create the sense of contrast that is the deciding factor of the particular form that we are trying to identify. the more changes that occur, the stronger the contrast and, of course, visa-versa.'
taking dr. murray's approach - i would say that i play less 'contrast' possibilities with mozart and haydn and more with say, brahms. particularly, i am thinking of the #2 intermezzo op. 118. you have a much more dramatic countermelody (as dr. murray stated) and you have to try harder to bring out this contrast - whereas - the contrasts of earlier works by what we usually term 'classical' composers (btw, i tend to think that brahms borrowed a lot from the classicists) were less dramatic and more lengthy. almost as if they were 'filling time.' more repeats, etc. etc.