The concept of musical functions is foundational to musical analysis, and essential to the understanding of musical styles.
A musical function describes the role that a particular musical element plays in the creation of a larger musical unit. Function is tied very much to the idea of expectation: given a certain element in a certain context, what element(s) is/are likely to come next? Likewise, how does a given element fulfill or deny the expectations set by what came before it?
A musical function typically has two defining features: the characteristics of the musical elements that tend to belong to that function (what notes tend to be found in the chord, for example), and the kinds of elements (or functions) that tend to precede or follow it in a succession of musical elements. Note that this is entirely dependent on the typical patterns of a musical style. Different styles of music may exhibit different functions or different behaviors for the same functions. The study of function and the study of style are inextricably linked.
The two musical traits most commonly studied for their functional properties in Western art and popular music are harmony and form. The study of both harmonic functions and formal functions will lead to an understanding of harmonic and formal syntax: the norms or principles according to which musical elements are combined into meaningful and stylistically appropriate successions. The study of harmony or form, then, is not a matter of learning to label chords, phrases, and modules correctly. It is a matter of interpreting the role that chords, phrases, modules, etc. play in the larger context in which they are found. That, of course, requires fluency in identifying (and thus labeling) individual musical elements. But identification is only the beginning of a much bigger, and more interesting, process of analysis. And it is that analytical work that will lead to true understanding of the pieces of music analyzed, and the styles to which they belong.
If a musical function describes the role that a particular musical element plays in the creation of a larger musical unit, then a harmonic function describes the role that a particular chord plays in the creating of a larger harmonic progression. Each chord tends to occur in some musical situations more than others, to progress to some chords more than others. These tendencies work together to create meaningful harmonic progressions, which can in turn form the harmonic foundation for musical phrases, themes, and larger formal units.
Generally speaking, the function of a chord concerns the notes that belong to it (its internal characteristics), the chords that tend to precede and follow it, and where it tends to be employed in the course of a musical phrase.
A theory of harmonic functions is based on three fundamental principles:
(Note the absence of root and quality from consideration here.)
Because tendency is style-specific, the same chord can have different functions in different musical styles. For instance, the kinds of functions we find in classical music are different from those we find in pop/rock songs from the Billboard charts. And though there are some general harmonic traits that are common to most eighteenth- and nineteenth-century Western composers (what we call the “common practice”), when we look in closer detail, we find some significant differences in the way Bach, Mozart, Brahms, and others compose their harmonic progressions.
Our initial exploration of harmonic functions will engage the general “common practice” that is shared by most eighteenth- and nineteenth-century Western composers. As we explore specific genres, composers, and works within that common practice, we will have opportunity to explore the more nuanced differences between composers, as well as to move beyond common-practice Western art music to include other styles, such as pop/rock.