Passage: There are many different methods of classifying musical instruments. Various methods examine aspects such as the physical properties of the instrument (material, color, shape, etc.), the use for the instrument, the means by which music is produced with the instrument, the range of the instrument, and the instrument's place in an orchestra or other ensemble. Most methods are specific to a geographic area or cultural group and were developed to serve the unique classification requirements of the group. The problem with these specialized classification schemes is that they tend to break down once they are applied outside of their original area. For example, a system based on instrument use would fail if a culture invented a new use for the same instrument. Scholars recognize Hornbostel–Sachs as the only system that applies to any culture and, more important, provides only possible classification for each instrument. The most common types of instrument classifications are strings, brass, woodwind, and percussion.

Question: Many different methods are used for classifying what?
musical instruments