The Universe of External Stimuli
First there is the universal set of all possible external stimuli.
The Language Prototype
Contained within this set is the Language Prototype, which consists of all "speech-like" sound patterns (and also some gestures).
The Native Language
The Language Prototype is the prototype for learning the infant's first language. It pre-classifies all external stimuli as either language or not-language, so that the infant can immediately start to learn language as a category of stimuli that have their own structure and rules, which must be learned as a set of structures and rules somewhat distinct from those that govern all other observable aspects of reality.
The native language might not be completely contained inside the language prototype.
But as long as the native language is mostly inside the Language Prototype, that will be enough for the infant brain to recognise the native language for what it is – and eventually the infant learner will recognise that those parts of the native language lying outside the prototype are indeed part of the native language.
Music
And then, finally, there is Music.
Music is contained totally within the Language Prototype, and is disjoint from actual languages (ie actual spoken language is not musical).
Music is defined by whatever rules define the Language Prototype, and by one simple additional rule. (This rule is something like: constant patterns of activity and inactivity in cortical regions involved in perceiving the language prototype.)
Caveat: Diagrams Not To Scale
If area is taken to be indicative of number of elements in a set, then none of these sets are drawn to scale:
- The Language Prototype, consisting of speech-like sounds (and some gesture-like arm motions), is much smaller than the set of all possible external stimuli.
- Any actual language is much smaller than the Language Prototype.
- Music is the smallest set of all, much smaller than both the Language Prototype, and much smaller than any spoken language (ie compare the number of possible tunes to the number of possible spoken utterances).