I have been trying to understand at least in part the structure of what is said in the challenges which helps me understand how the jigsaw pieces can be re-used in different contexts (and in my case helps me remember them a bit better in the first place). There is one thing I haven’t nailed down - I’m sure you can clear this up for me in 2 secs - in the challenges what sounds like “O’n i moyn” is used for ‘I wanted’. This seems like imperfect or ‘was’ + ing, type of grammar but has an ‘ed’ or past tense outcome. Can the imperfect have this outcome in Welsh for some words (do you just have to learn them)? If this is the case then what I originally thought was “Of hi’n moyn” when I first listened on the challenges, will actually be “Oedd hi’n moyn” - is that right? Thanks in advance Rich
(O’n i’n moyn)
That’s pretty much right Rich. To want something is a ‘lasting’ concept so ‘was’ is used.
I’m sure the grammarians will be along to explain it but I would say just to go with that, there are more words that are treated the same but not many.
Ok great, thanks for the reply. I guess there is quite a fine distinction between ‘I was wanting’ and ‘I wanted’ - I don’t think I’ve thought so much about tenses in a very long time!
I see, so having re-read that I have appreciated the depth of the answer - so it makes a difference if there is a lasting concept. I’ll think about that & work on it! Thank you.
My Cornish teacher gave as an example the sentence, “When I saw his new sports car, I immediately wanted one as well” as an example of where the “normal” past of “to want” might be appropriate – because the wanting there is sort of a point-moment “action”.
But in general, wanting is continual rather than a single one-time action like opening a door, and so in Cornish as well, the normal past for “want” is the imperfect.
Welsh may be similar.
I agree with @gruntius (fel arfer 
) Moyn, eisiau, gwybod, nabod - wanting and knowing, are both concepts in Welsh that last. So they’re “imperfect” (i think, although grammar is not my forté).
Correct, @AnthonyCusack - they are called stative verbs, because they are states, not actions; and in Welsh stative verbs in the past have to be in the imperfect rather than the preterite (= simple past). Unlike English, which is what causes the difficulty.
Verbs like perthyn belong and cynnwys contain are similar examples.
In English it’s the PRESENT tense that makes a distinction between stative and action - stative verbs generally don’t use the present continuous. We don’t say: This box is containing three items, any more than we say I am knowing Alfred.
So (generally!) you can tell if a Welsh verb CAN’T be used in the preterite by seeing if the English equivalent CAN’T (generally!) be used in the present continuous! 
Good trick - breaks the ice at parties!!
You know the answer now, but just to add “meddwl” to the list of verbs for which you’d use the continuous past rather than the simple past. (At least I think so, although “thinking” could be described as an action, I suppose).
It certainly fits the rule of thumb that “if you wouldn’t use the present continuous in English” – I wouldn’t say “I’m not thinking so”. (But I would say “I was thinking we could get her a cactus” or “Are you think what I’m thinking”? Help!)
I wonder how caru fits in, because despite what McDonalds would have us believe “I’m loving” doesn’t sound natural to me - I would say e.g. “I love skiing” or “I love my daughter” and not “I am loving it/her”. O’n i’n caru nofio pan o’n i yng Nghymru “I loved swimming when I was in Wales”?
I wasn’t sure whether I would actually get an answer, so I’m a bit blown away by the response! Thank you everyone - I’m very grateful for you taking the time to reply.
I’ve only had this question for several weeks - should have asked it sooner, ha, ha! (But on the other hand I’ve answered about another 30 myself in that time frame so I’ve saved you a lot of dumb questions, ha, ha!)
I got these answers from a book written by someone called Gareth King!?
Oh, it’s a very common name… 
But he is not a common man!
You are certainly right, @mikeellwood, that meddwl is generally used with an imperfect - o’n i’n meddwl - I thought. Though you DO sometimes hear the preterite with this verb - e.g. meddlylies i . Now, my feeling is that this is NOT natural Welsh, and is probably due to English influence. A bit like hoffes i for o’n i’n hoffi - I liked - sounds dreadful to me, but you do encounter it, again underlying English patterns are responsible I suspect.
Think is generally regarded as a state rather than an action - at least much more the former than the latter!
It’s a) an Americanism, but more importantly b) with a specific non-state meaning, isn’t it? I’m loving those shoes of yours means something like ‘I have spotted those shoes you’re wearing just now, and I am experiencing a sudden feeling of love as a result’. ‘Ongoing state’ characteristic of the verb 'love (as in I love Nutella) switched OFF in this meaning (sudden feeling of love, see?), and therefore present continuous is allowed.
Didn’t some one say, “I think, therefore I am” to define being human? Descartes certanly did not see it as an action!l
Edit
Just saw comment about loving. I am loving, to me, describes me as a caring person, just as, in Descartes’ definition, “I am thinking”;defines me as human!
Yes - though of course that is [verb be + descriptive adjective], rather than [continuous present of verb love ], which is what the McDonalds usage is.
Just saw the end of a BBC headline that said “gwerthu allan o fewn oriau”. I don’t know what it is and I understand what it means, but it just felt slightly odd to me seeing such a literal translation from English, in terms of words and grammar.
Gad i mi ffeindio allan ar dy gyfer di
I’ve seen meddyliais in written Welsh a few times, is it considered formal language?