I don't think the verbal particle yn is the same as the preposition yn that means "in"... they don't do the same mutations, for starters.
And it might be better to translate mae as simply "is" in this sort of sentence - "Is the butterfly PART orange" with an untranslatable verbal PARTicle.
Yes, that works much better. It is only that although we would not say that for a butterfly, we often say that something is available in orange, or black or white or red, etc. We could even say that someone is dressed in orange. So, that it is possible that there was a parallel there somewhere at one time. It is not the same as the preposition "in", meaning a physical location, either.
As I said, it's there for grammatical reasons, to link the predicate adjective "orange" to the copula "to be".
It's kind of like the "do" in English questions such as "Where do the children want to go?" -- it has no "meaning" as such and is there just for grammatical reasons: because English questions require that word in that situation.
So also Welsh yn is a grammatical word that is required in some situations, where a predicate adjective, noun, or verb is connected to the verb "to be".
You can't leave out the "do" (*"Where the children want to go?") from the question above, nor can you leave out the yn (*Mae'r pili-pala oren - which would be "The orange butterfly is").
Continuing from the last example, compare these:
- Mae pilipalod yn oren. = Butterflies are orange.
- Mae pilipalod oren. = There are orange butterflies.
Having the yn separates the oren from the pilipalod and makes it clear that it's a predicate adjective rather than an attributive adjective.
The reasons are:-
When we added this word we didn't have an 'n available to use in the sentence.
Sometimes you don't contract the yn for emphasis:-
Mae'r pili-pala'n oren = The butterfly is orange
Mae'r pili-pala yn oren = The butterfly IS orange
The English to Welsh translation accepts both as the best answers.
I (non-native speaker) would say: “Dyna pili-pala oren.” dyna means something like “there is, see there” (i.e. it calls the listener’s attention to something). I would only use mae as “there is” when you also name the place: “Mae pili-pala oren ar y blodyn hwn.” (There is an orange butterfly on this flower.”
To analyse the example sentence above: Mae [is] ’r [the] pili-pala [butterfly] yn [a grammatical particle] oren [orange]. The particle yn is used between the subject and the predicate of the sentence.* If you want you can memorise the pattern: mae x yn y = “x is y”.
* Or rather predicate minus theconjugated verb form (in this case mae) which appears at the beginning of the clause.