Fungible is the property of an instrument having various parts, or the instrument itself, easily replaceable with another that are indiscernible from the original.
An example is being able to buy a commercial plastic recorder and swapping out any part (or the whole instrument) with the same model and have it function exactly the same. An important conceptual feature of this fungible property is that the original instrument and the replacements are indiscernible from one another. In some cases there is no original.
The use of fungible parts is common with DIY instruments that use common household and hardware store materials such as soda bottles, pvc pipe, cans and lids. Fungible instruments can sometimes be made solely from a set of instructions and assembled from these easily accessible parts. This is a common strategy for instrument builders who want their instrument widely distributed with players who are interested in their instrument. Instruments that employ this strategy shift focus away form the instrument being a important or unique object, and instead are focused on making the sound qualities easily reproducible. This is also a common feature of commercial instruments that are sold as products, mostly for the purposes of making them easily reproducible and makes it so that parts can easily be replaced when broken. Generally this is not the reason for calling an instrument fungible on this wiki. This term is more intended for when an instrument maker makes an instrument that is fungible in a conceptually relevant way.
The instrument of Dennis Havlena, Nicolas Bras, and of Bash the Trash often have fully fungible parts, and are made as simple as possible to allow for others to be able to easily build a copy of their own.
The instruments of Zimoun are an excellent example of a fungible instrument where the use of commercial replication and being fully fungible is conceptually relevant to the work. Though his installations are fine art objects they are made a large swarms of near exact copies, using mostly commercially available materials like cardboard boxes and stepper motors. If any one instrument in a Zimoun installation is replaced with another copy it would be virtually impossible to tell and the individual instruments present are not important as a unique object, but instead important when considered in mass as indistinguishable copies of one another.
As shown above in the Zimoun example these swarms of boxes can be fungible when each individual box is replaced with a separate copy the swarms individual instruments become hard to discern from one another, to the point of being Indiscrete. Alternatively individual boxes can be removed or added to the swarm would still be a swarm, and this makes the total number of boxes in the swarm fungible as well. This definition is slightly different in that some works can have the overall amount changed and it still is difficult to distinguish the change.
Replaced parts being difficult to differentiate from the original is important to the concept of something being fungible. Fungible objects cannot generally have their parts replaced with ones that alter the color, size, material, or shape of the object. The replacement generally needs to be as similar as possible to the original. There can be a scale of how fungible something is, where the more difficult it is to tell the more fungible it is.
Instruments made with easily replaceable parts or are made out found objects are often also Indiscrete.
There is sometimes a heightened importance with the way the instrument is interacted with when it is fungible.