Plain language phrase for a group whose members are not interchangeable

Question

There is a well known part of speech called "adverbs". However, many adverbs are not grammatically interchangeable with each other. From Wikipedia:

Adverbs are traditionally regarded as one of the parts of speech. However, modern linguists note that the term "adverb" has come to be used as a kind of "catch-all" category, used to classify words with various different types of syntactic behavior, not necessarily having much in common except that they do not fit into any of the other available categories (noun, adjective, preposition, etc.)

Adverbs as a "catch-all" category

• She gave birth naturally.
• Naturally, she gave birth. different meaning of "naturally"
• Perry is very fast.
• *Perry very won the race. only some adverbs can go in this position
• The sock looks good there.
• *It is a there beautiful sock. only some adverbs can go in this position

What can we call groups like this?

Adverbs are not always grammatically interchangeable because they are ____. This means we have to classify this word group into specific subgroups before they can be truly useful.

I'm looking for a generic term, not one specific to linguistic terminology. Noun, adjective, it doesn't matter. Feel free to completely reword the example sentence as long as the phrase is relatively simple. It would be good if the phrase could also be used as a label:

Adverbs (____)

Heterogeneous has the meaning I want (not all the members are the same, but some can be; different from all members being different), but neither it nor any of its single word synonyms are plain enough for me:

• Wiktionary Thesaurus:heterogeneous
• thesaurus.com: heterogeneous
• synonym.com: heterogeneous

I think it's unlikely a single word will get the meaning across in a way that most people would understand, so a phrase seems more likely. The best I can come up with so far is "uneven group":

Adverbs (uneven group)

Adverbs are not always grammatically interchangeable because they are an uneven group.

Answer 1

Adverbs are not always grammatically interchangeable because they are not of a kind. This means we have to classify this word group into specific subgroups before they can be truly useful.

1998 Sterling Dictionary of Idioms Vijaya Kumar (a) They are of a kind, exactly like twins in their behaviour. (b) The boys living in that street are of a kind and I wouldn ‘t advise you to mix with them.

OED

Kind 8.a. A class or category of things distinguished by common characteristics and attributes possessed by its members; (usually with of) each of the subordinate classes into which a specified class can be divided; (later also more generally) a particular variety or type; a sort. Now the usual sense.

1732 G. Berkeley Alciphron I. ii. vii. 85 Suppose you saw a fruit of a new untried kind.

1915 J. Buchan Thirty-nine Steps vi. 136 I tried the shutters, but they were the kind that lock with a key and I couldn't move them.

1960 Protection - Volumes 83-84 - Page 21 The thing to do, you might suggest, is to buy socks all of one kind.

Answer 2

I just stumbled across a set of words that I think will do the job, even though they're not everyday words:

• monophyletic
• paraphyletic
• polyphyletic

These words are used in descriptions of evolutionary trees: monophyletic groups of species are all species descended from the same ancestor (a complete group), paraphyletic groups are all descended from the same ancestor but are missing one or more species (an incomplete group), polyphyletic groups have traits in common that their most recent common ancestor didn't have (a mixed group).

I see no reason why these words can't be used to describe things outside of biology, so adverbs form a polyphyletic group.

Answer 3

I can't think of an offical/recognised term for your "Adverbs (_____)" request, but maybe "Adverbs (situational)" would cover it?

Bringing chemistry into it, maybe adverbs that can exist in more than one situation with the same meaning (the opposite of your examples) could be referred to as allotropic, so possibly "Adverbs (non-allotropic)"?

Ultimately though these are just my musings on a topic that I stumbled across and piqued my interest, and I agree with @High Performance Mark that rephrasing is the least ambiguous way to get the point across.