From the previous comments, what I understand is that ei is an additional possessive pronoun that stands before the verbnoun, which is not related with 'you', being ei a pronoun for the 3rd singular person.
Having said this, I have a couple of doubts about the use of this ei.
1) Is ei invariable when used before meddwl (or, better, feddwl)?
In other words, if a different person was used, e.g. 'he', or 'you' (plural), would the sentence be respectively:
Beth mae e'n ei feddwl?
Beth dych chi'n ei feddwl?
or would ei change in some way?
2) Do other verbnouns take this peculiar construction, or is it unique to meddwl?
Thanks in advance!
Good question! Ready for a long answer? :D
To start with, remember how to say the following in Welsh:
Rwyt ti'n meddwl "You think"
Rwyt ti'n ei feddwl e "You think it" (masculine)
There's also the more formal version of the last one:
Rwyt ti'n ei feddwl "You think it" (masculine)
To say "What do you think?", in Welsh there are two parts:
Beth + Rwyt ti'n meddwl "What" + "You think"
Beth is masculine (it's from pa beth "which thing", and peth "thing" is masculine). When the two halves of the above sentence are joined together, the change that takes place in the second half is that something is added to refer back to the beth at the beginning. As beth is masculine, this is logically going to be ei (masculine), hence:
Beth rwyt ti'n ei feddwl? "What do you think?"
It's the ei that connects the second half to the beth which it refers back to. It's as if it glues the beth to rest of the sentence. Think of a big red arrow from the word ei pointing back to beth - that's it's function.
The same would be the case if you stick anything masculine at the start to be referred back to. And bearing in mind meddwl can mean "mean" as well as "think", the possibilities are endless, whether questions or statements:
Pwy rwyt ti'n ei feddwl? "Who do you think/mean?" (pwy is masculine)
Fe rwyt ti'n ei feddwl "You mean him"
Hwn rwyt ti'n ei feddwl "You mean this" (masculine)
Steffan rwyt ti'n ei feddwl "You mean Steffan"
So if you have a feminine or plural noun at the start, obviously the pronoun (and its mutation) would change:
Hi rwyt ti'n ei meddwl "You mean her"
Hon rwyt ti'n ei meddwl "You mean this" (feminine)
Sali rwyt ti'n ei meddwl "You mean Sali"
Nhw rwyt ti'n eu meddwl "You mean them"
Y rhain rwyt ti'n eu meddwl "You mean these"
Fy mhlant rwyt ti'n eu meddwl "You mean my kids"
The above are all emphatic sentences i.e. not normal verb-subject-object ones. When you emphasise something in Welsh, you send it to the front, but it's the little words like ei that then appear, referring back, glueing it to the rest of the sentence. The ei takes its place now that a word like beth or Steffan has gone for a wander to the front!
If you change the subject, verbnoun or even tense, the same principles apply:
Beth mae e'n ei wneud? "What does he do?"
Pwy dych chi'n ei weld? "Who do you see?"
Sali dw i'n ei gweld "I see Sali"
Y gloch dyn ni'n ei chlywed "We hear the bell"
Y llythyrau roedd hi'n eu hanfon "She was sending the letters"
Ci byddan nhw'n ei brynu "They will buy a dog"
Cath byddan nhw'n ei phrynu "They will buy a cat"
Llygod byddan nhw'n eu prynu "They will buy mice"
Hopefully you can see the same pattern in all the above.
One final point is that the use of this little pronoun ei or eu is usually found in more formal language. If you drop the pronoun, the sentence becomes less formal and more colloquial, especially when you drop the mutation too. The following all mean "They will buy a dog" but they get less formal as you go down:
Ci byddan nhw'n ei brynu
Ci byddan nhw'n brynu
Ci byddan nhw'n prynu
Our original sentence "What do you think?" has a number of possible translations depending on how formal you want to be. Again, from more to less formal:
Beth rwyt ti'n ei feddwl?
Beth rwyt ti'n feddwl?
Beth rwyt ti'n meddwl?
It's also acceptable to use wyt after beth in this instance, which is less formal than using rwyt:
Beth wyt ti'n ei feddwl?
Beth wyt ti'n feddwl?
Beth wyt ti'n meddwl?
As I say, we're dealing here with more formal Welsh, something which Duolingo covers very little of, and something which can get quite involved and nitpicky (but really interesting in my opinon!). Rest assured that in colloquial Welsh forms like Beth wyt ti'n feddwl/meddwl? are all you need.
Anyway, all that's a lot to take in. Just let me know if anything's unclear. I'm always happy to help.
I really appreciate such long answers; actually, I save them in my grammar files, for future reference. Thank you very much for taking the time to write down all this (with a neat layout too!).
All explanations are perfectly clear.
The main difficulty for me is that as far as I have progressed along Duolingo's tree, some topics have not been dealt with yet. So although I do understand the explanation, I still lack the theoretical basis of some constructions.
In particular, I have not yet learned the use of direct object pronouns, so in the construction
Rwyt ti'n ei feddwl e
the use of ei + verbnoun + e is new to me.
So far, I have only learned ei + noun + e as part of the possessive construction.
However, I realize that in an interrogative sentence that starts with a question word such as beth or pwy, the pronoun ei can stand before the verbnoun, and since it points back to the opening question word (what gives reason for it being a 3rd person pronoun), it agrees in number with beth and pwy, which are masculine. But even if they were feminine, ei would be used all the same, because it fits both genders (only the type of mutation to which the following verbnoun is subject would be different).
Also the emphatic construction with verbs and tenses else than yw or ydy is completely new to me.
But I realize that the noun (subject) stands before bod. So when the subject is plural, the pronoun used before the verbnoun turns into eu (plural, for either gender, which brings no mutation to the verbnoun).
I also understand that the use of ei / eu before the verbnoun and the relevant mutation has to do with the degree of formality; I have barely scratched the surface of this topic by now.
It might take me a long time to 'digest' all these topics as I make further progress, but your explanation will provide a very valuable stepping stone!
P.S.- One last doubt about the sentence Y llythyrau roedd hi'n eu hanfon.
Wouldn't this translate as "She was sending the letters", rather than "They were sending the letters"?
Yes, you've grasped it well even if some of the points are new to you. It takes time to digest as you say, but hopefully as you progress through the course and come into contact with more Welsh, things will start feeling more normal. You seem from your questions and comments to be a very capable learner, so keep at it and you'll go far. Thanks too for the heads-up on Y llythyrau roedd hi'n eu hanfon - I've corrected it now.
Croeso. "What do you think of it?" would be:
Beth rwyt ti'n meddwl amdano fe/fo? for a masculine "it"
Beth rwyt ti'n meddwl amdani hi? for a feminine "it"
As stated above, it's less formal (and more normal!) to you wyt rather than rwyt, but I've included the fuller form for completeness' sake.
I'm not sure how to explain it myself other than "it can be used in this sort of sentence that starts with beth? 'what?'."
And even if you don't use it, the mutation it produces may still be heard, i.e. you might hear Beth wyt ti'n feddwl? or Beth wyt ti'n wneud?, with a soft mutation of meddwl, gwneud to feddwl, wneud after the optional ei.
I'm sorry, I meant: can you explain what the English translation means. I have suggested two English phrases I thought might be the same but you have implied that they are used in some kind of different context... so I'm asking what your interpretation of what "What do you think?" is meaning ... I hope this is okay.