In fact, it is not possible to classify Esperanto without distinguishing at least three planes: intrinsic, intermediate and extrinsic. To define to which plane one or another language trait belongs, we shall use the following criterion: a given trait is considered as belonging to the extrinsic plane if a change can be introduced in it without giving to the speakers, generally, the feeling that the language is altered in its essence or in its identity; it is considered as belonging to the intrinsic plane if a change in it creates the feeling that the language has been fundamentally altered.
From this point of view, the quality of the sounds is an extrinsic trait. No one feels the language very different depending upon whether a speaker has an Italian or a Danish accent in Esperanto. In both cases, Esperanto remains Esperanto. In the same way, English remains English, whether it is spoken with a British, Indian or American accent. To substitute one word for another does not call forth a sense of an important change either. We do not have the feeling that we are speaking a different language if we switch from
“My father did not want her friend to use his novel automobile” to
“My dad did not wish her pal to use his brand new car”.
The given arrangement of sounds that expresses a concept we can therefore regard as an extrinsic trait.
When we reach the level of word order, the impression that we are changing the language becomes more acute. If I say My father wanted not that her friend use the car brand new, I arouse a sense of strangeness. But nevertheless this change does not render the language completely foreign. It remains English, even though perhaps poetic or archaic. We have reached a more interior plane than that of the sound system or the roots, but we are not yet at the kernel. Syntax is somewhat closer to the center. The phrase My father he wanted not that her friend she used of the brand new car sounds more foreign than the other just presented.
And yet we do not have the same impression that the language has been attacked in its very identity as we would encountering such phrases as I’s fatherman ha-unwill she’s friendman go-use he’s new-new earthing or Fatherem no willis friendha usu newan caron. These sentences are no longer English, despite the fact that nearly all the roots have been preserved and that the phonetic system need not be changed to pro-nounce them. Why? Because this time we have assaulted the intrinsic plane, that of fundamental grammatical conception. The verb system, the possessive adjectives and other traits are quite different from even archaic, poetic, regional or mildly foreign English.
Proof that this plane is more fundamental than that of the forms of words we can take from the following point: the average speaker of English feels that a phrase as My moffy did not sut her shramp to gose the insable flar, although incomprehensible — it means nothing — might nevertheless be some kind of English or of English slang (in other words, it does not attack the identity of the language), whereas the sentence presented above Fatherem no willis friendha…) strikes even those who can decipher it as belonging to another linguistic universe.
Accordingly, we can distinguish the following language planes:
1) The kernel or intrinsic (fundamental, essential) plane: the basic type of grammar and of derivation, i.e. the manner in which the relations between words are indicated (e.g. which determines which), the details about this or that nuance (whether a thing is singular or plural, whether it is completed or continues, etc.), and the relations between the concepts (for example between ‘brother’ and ‘brotherly’, between ‘avoid’ and ‘unavoidable’, or among ‘hair’, ‘split’ and ‘hairsplitter’);
2) the intermediate plane: syntax and customary word order;
3) the extrinsic plane: the actual forms of words and the system of sounds.