Why are woodwinds and brass instruments not accurately classified by the materials they are made from?

Classifying musical instruments by the material from which they are constructed is inaccurate because it fails to account for the actual method of sound production, which is the defining characteristic of an instrument's function.12

The terms "woodwinds" and "brasses" are conventional labels used primarily within Western orchestral contexts, but they do not reflect the physical composition of modern instruments. For example, many modern woodwinds, such as flutes and saxophones, are constructed from metal rather than wood. Conversely, historical ancestors of modern brass instruments, such as the cornett and the serpent, were typically crafted from wood.132

To address these inconsistencies, musicologists use the Sachs-Hornbostel system, which classifies wind instruments as aerophones based on how they produce sound. Under this system:41
* Woodwinds are defined by the use of an edge (flutes) or a reed to initiate the vibration of an air column.13
* Brass instruments are defined as lip-vibrated instruments, where the player's vibrating lips against a mouthpiece initiate the sound, regardless of whether the instrument is made of metal, wood, or horn.2