Long ago, when I was in primary school, I was taught that musical instruments come in four varieties: strings, woodwinds, brass and percussion. It doesn’t take a very profound analysis to recognize that there’s a logical problem with this categorization system: The criteria are not consistent from one category to the next. One group is identified by the primary sounding element, two by the material the instruments are made of, and one by the method of activation. As noted by Curt Sachs (one of the early scholars of musical instruments), one might as well divide Americans into Catholics, bankers and Californians. But the system didn’t arise because it was logical; it arose because it fit the practices of the music culture in which it evolved — namely, the culture of European classical music that school-kid me was ostensibly being taught to appreciate. Indeed, every culture that has enough instruments to categorize creates taxonomies for them, using various criteria as suits the culture’s traditions and music-making practices. For an extensive cross-cultural review of this topic, read On Concepts and Classifications for Musical Instruments by Margaret Kartomi.
Meanwhile, the desire has persisted for a logically coherent categorization system for musical instruments that is universal and independent of cultural context. Indeed, many attempts have been made to make such a system, and the question of categorization remains an ongoing topic of discussion in organological circles. (Organology is the academic term for the study of musical instruments. In college, when I first encountered the term, I had a roommate who coincidentally was taking a class in penology, but it turned out that the two fields were unrelated.)
Among organologists in the academic world, a lot of attention goes to this question of taxonomy. Perhaps this is because it gives them something to talk about that seems kind of analytical; not just descriptive. And it’s true that the creation of such systems is an interesting and challenging intellectual exercise. Thinking about categorical delineations in a rigorous way can stimulate real thought which in turn provides greater insight into the subject at hand. It can even foster creative rule-breaking.
Among the musical instrument taxonomies that have been devised, one has come into widespread use. This is the Hornbostel-Sachs system, developed in 1914 by Curt Sachs and Erich von Hornbostel. Their work was based in part on a previous system devised by the Belgian ethnomusicologist Victor-Charles Mahillon. In Hornbostel-Sachs, each instrument is assigned a decimal number similar to the Dewey Decimal numbers used for books in libraries, with each digit from left to right representing a branching series of increasingly detailed distinctions. The first digit, representing the broadest level of differentiation, corresponds to the nature of the initial vibrating body. It gives us these four categories: aerophones (wind instruments), chordophones (string instruments), membranophones (drums — or, more specifically, instruments in which the initial vibrating body is a stretched membrane), and idiophones (instruments in which the initial vibrating body is inherently rigid). This question of rigidity is an interesting one: regarding the first three types, notice that strings and membranes, lacking inherent rigidity, depend upon externally applied tension to function acoustically; nor is air itself rigid but in most cases calls for some kind of tube or vessel to contain it. It is idiophones alone that are in themselves rigid and vibrate in a way that depends on that quality.
Subsequently, by general agreement, a fifth category has been added under the term electrophones (instruments in which the initial oscillation is that of electrons in an electrical circuit).
Beyond this first level of differentiation, the criteria are different for each category, as the distinctions to be made differ from one instrument type to the next. For a run-down of the full system, you can look to the Wikipedia page. As you get farther into the system the details become increasingly arcane, but in the larger world one of the main influences of the Hornbostel-Sachs system has been to establish those four (now five) primary categories in the language.
Meanwhile, subsequent academics have tinkered with the system, proposing amendments or additions intended to remedy various shortcomings. People have also occasionally proposed entirely new systems, although none of these have so far come into widespread use. For instance, in his 1971 textbook The Ethnomusicologist, Mantle Hood outlined an elaborate methodology for organizing the information about the various instrument types into a complex symbolic notation, as a way of systematizing the information. Among the essential data he embedded in each instrument’s “organograph” was not only physically descriptive information, but also considerations of social context such as whether the given instrument is one of high or low prestige, or whether it is associated with one or another gender. (This naturally reflects Hood’s interests as an ethnomusicologist.)
Let’s step back for a moment and look at what an ideal categorization system for musical instruments would look like. The goal, I think, would be a system in which any musical instrument could be given a unique assignation within the system, based on criteria which are unambiguous, consistent and logical. You’d want the system to be logically exhaustive, meaning that not just the instruments the taxonomist is familiar with, but every logically possible musical sound device — every odd instrument you might find in some remote culture, as well as whatever off-the-wall thing someone might dream up tomorrow — could be accommodated in a unique and non-arbitrary way. To achieve this, the person who devises the system would have to think lucidly about the very essentials of musical sound-making.
But here’s the thing: reality — in this case, the reality of the many ways one can make potentially musical sound — does not always cooperate with the taxonomist. It’s not just that someone may at any time come up with some new idea that doesn’t readily fit the pre-ordained structure. It’s that distinctions that look clean on paper often turn out to be sloppy and ambiguous in the real world. A prominent example from Hornbostel-Sachs is reed instruments. Reeds are classified as aerophones, suggesting that the initial vibrator is air. In this thinking, the reed itself is considered to be an air-gating system; not the primary actor but, as it were, an enabler. But, gee… isn’t it at least arguable that the reed should be seen as the primary vibrator? It is, after all, the vibration of the reed that instigates the vibration of the air, and the pattern of its movement is the starting point for the resulting tone quality. If you see things that way, reed instruments would have to be categorized as idiophones. Thus, when it comes to fitting the physical reality to the prescriptions of the categorization system, blown reed instruments present at best an ambiguous case.
As another example, how about longitudinally vibrating strings? (For an example, see here). They certainly look like strings (though typically much longer than conventional strings), so it might seem that they should be called chordophones. But explicit in the definition of chordophones is the notion that strings are held at tension. Although longitudinally vibrating strings are typically held at least somewhat taut from each end for mounting purposes, the tension is not acoustically important and changes in tension do not affect the sound. This reflects the fact that such strings function in an entirely different manner from conventional strings. From an acoustical perspective, they are more closely related to wind instruments — that is, the physical pattern of the oscillation is quite unlike that of other strings, and closely parallels that seen in tubular winds. On the other hand, perhaps they should be seen as idiophones, since in this unusual case it is the inherent rigidity of the material of the string itself that perpetuates the vibration. Thus, here again is a case that becomes ambiguous when you try to apply the Sachs-Hornbostel category distinctions rigorously.
Then, of course, there are hybrids: instruments which use more than one type of initial vibrator. This isn’t especially difficult to groc conceptually, but it does make it difficult to decide which room in the Hornbostel-Sachs museum they belong in.
… And when you get to the end of this essay, you’ll see a few more examples representing the difficult-to-categorize contingent taken from my own collection of instruments.
My intention here is not to quarrel over details, nor to resolve past disputes, nor to throw monkey wrenches, but just to say: the world of potential musical sound makers is wonderfully messy. Categorization systems are practically useful and intellectually stimulating, but in their fit to reality there will always be a few square pegs in round holes. The most interesting stuff will often be found in the ambiguous interstices.
Bringing this discussion home: There are over a hundred different instruments appearing in the instrumentarium section of this website, and I have had to figure out how to organize them for presentation. In what sequence, and grouped how? My initial inclination was not to categorize them at all, but just to present them in one big batch without sub-groupings, in a sequence following no logic beyond a vague aesthetic preference. But I feared that such an undifferentiated mass would be too un-navigable for visitors to the site. Alternatively, I could have organized them in a manner in keeping with the Hornbostel-Sachs system. But I found, in attempting to apply it, that it didn’t sit well with the contours of my collection. So I grouped them in a way that roughly reflected my building practice, yielded reasonably similar group sizes, and fit with some subjective associations of my own. For instance, I’ve made a lot of things that qualify as zithers, so OK, I said to myself, I’ll make that a category. Similarly, tubular wind instruments feel to me like a separate group from my other oddly shaped and oddly functioning aerophones, so I treated those as two separate categories.
Near the end of the list on the instrumentarium page there’s a group called “uncategorizables.” Some of these are instruments that really do stand outside of recognized categories. For instance, the one called waterfall involves long floppy metal bands fixed at one end and free at the other. Despite the fixed-at-one-end consideration, this is clearly not a lamellaphone, which implies rigid elements. But none of the other standard categories seems to relate any better. Another example: Savart’s wheel illustrates what I call forced vibration, as opposed to the naturally springy sort of oscillation that is characteristic of most other musical instruments. It’s hard to see forced vibrators as members of any of the usual categories: the primary distinctions in Hornbostel-Sachs are based on the properties of the initial vibrating materials, but with forced vibrators the nature of the vibration is relatively independent of the inherent acoustic properties of the materials they’re made of.
On the other hand, several of my “uncategorizables” are in that group not because they’re so innovative, but just because they’re hybrids. Like the one called Stringtine (aka springtime) or the ostinato machine, they use elements of more than one type. Rather than arbitrarily placing them in one category or the other, I just dumped them into the uncategorizable bin.