Different linguists therefore take different approaches to the problem of assigning sounds to phonemes. For example, they differ in the extent to which they require <answer>allophones</answer> to be phonetically similar. There are also differing ideas as to whether this grouping of sounds is purely a tool for linguistic analysis, or reflects an actual process in the way the human brain processes a language.
The phonetical similarity of what thing causes disagreements between linguists?
allophones