What characteristic of letters is considered stable?

The characteristic of letters that is considered stable is their name. Each letter of the alphabet has a specific name, such as "A," "B," "C," etc., and this remains consistent across languages that use the Latin alphabet. The name of a letter is a fundamental aspect of its identity and does not change regardless of pronunciation, usage, or context.

In contrast, the visual appearance of the letter can vary due to different fonts and handwriting styles, which can change how the letter looks. The sound associated with a letter can also vary significantly depending on the language and the surrounding letters, leading to different phonetic pronunciations. Lastly, the context in which a letter is used can alter its meaning or function, especially in languages with complex orthographic systems. Thus, it is the name of the letter that provides a stable and reliable reference point in understanding the alphabet.