Can you give examples to such synonymous pairs?

"Phonological process" is not necessarily conscious, but more like "used rather consistently" among speakers of a dialect.

I'm not entirely sure what you mean by 'synonymous'. Do you mean 'spelled identically' in phonemic transcription? Like, for example, English 'bet' and French 'bête', or English 'how' and Mandarin 'hao'? And how would you find out how many categories there are? Is your second case be something like a stable output that is somewhere between the two?

No, besides a similar form they also have to have the same meaning!

Like English "sure" and French "sûr" in, say, 1) a Canadian community which used to be French-dominant and is growing English-only speaking, or 2) one in a more stable bilingual situation.

In that case, I am interested in questions like, do speakers A) keep alternating well distinct forms (eng. sure) vs (fr. sûr) and the percentage of use gradually changes until total replacement or B) would a continuity of fusion-forms be created and used in code-mixing utterances, like the "s" becoming more and more palatal or the [y] articulation moving back gradually.

May some speakers proceed by alternating (A) and others by fudging (B)? May some communities proceed by alterning and others by fudging?

And, above all, can we expect in a social situation like (1) more behaviours like (B) because B is a "more silent" process and therefore more likely to result in permanent change?

Many thanks!!

P.S. I know the English-French code-mixing example is not so well-chosen because the languages are so different...I chose that to make it more universally understood

But just try and think of any local variety of a standard language with variation of one word in the standard vs dialect dimension, the two variants differing by just one feature of one phoneme (or should I say allophone, as it distinguishes languages but not meaning?) and see whether this is standardizing (1) or maintaining variation (2) and whether variation among bi-dialectal speakers is of type (A) or (B) described.

Interesting but complex questions! Without going into any of them directly, I would like to mention an unpublished (and now lost, alas!) paper I wrote on the ability of a speaker who made the COT:CAUGHT distinction regularly and natively, to distinguish it after having lived among speakers who lacked it. The surprising result (to me) was that the speaker failed to recognize the distinction when listening to recorded word lists. I am sure that I have seen this point documented elsewhere, but I don't recall where just now. The moral is that what happens in production does not necessarily always mirror what occurs in reception. (Sometimes the result runs the other way: the hearer recognizes the distinction in the speech of others, but does not produce it -- pointing to the hazards of making internal psycholinguistic inferences based on external events.)

    --Rudy

Thank you, a very interesting result indeed. And it further complicates the matter.

Not to mention that the same auditory/observable outcome can be obtained by categorically different articulatory strategies...

Better to introduce my case, perhaps: it is in the field of intonation. In my community we have a dialect-like accent, realizing a rise-fall pattern with a high peak well aligned in the pretonic vowel and a standard-like accent, with a peak well aligned deep inside the tonic vowel. We use them both, indistinctively, probably with the unique socio-phonetic different value of "being speaking with an accent or not", both for contrastive focus statements and for information-seeking yes-no questions, the difference between the two sentence types being elsewhere in the utterance (boundary).

But as time goes on,  ONLY for questions, youngsters have "silently" converged the two patterns into a unique midway accent, with one high peak aligned in the midway position of syllable boundary/tonic onset; whereas for contrastive statements, both strategies "pretonic peak" and "tonic peak" are surviving change in their purest form and a third accent, with a double peak (pretonic + tonic) appears here and there but it does not seem bound to prevail. That is, only for contrastives, speakers are maintaining the categorical distinction of being or not speaking with an accent.

In intonation, phonology is not usually the interface phonetic/semantics but rather phonetic/pragmatics.

So, first of all, and this is just a terminology issue, I don't know whether the categorical distinction "speaking or not with an accent" can be called phonological because on one hand it is not contrastive in meaning/information, but on the other hand it is discrete and "speaking with an accent" affects pragmatics to the extent that the speaker is either choosing to speak with an accent or, even when this isn't done "on purpose", the listener clearly perceives that the other is speaking with an accent. Probably "socio-phonological" will do.

But the main point is, may I assume that the only-phonetic convergence of questions, just for being gradient, is in some respect more "unaware"? Is there any study assessing this in a similar situation? Matched guise-type, perhaps?

I want to relate my findings to the hypotheses (see Trudgill on Sayers 2014) according to which change that happen below the level of consciousness are more likely to result in permanent change, as it seems to be in my case. And I would like to (and I wonder whether I can) define a process as more "unaware" (and it seems reasonable to me) just for being only-phonetic non-"socio-phonological" and gradient.