I am confused about Relative Clauses! The ‘who’ or ‘that’ link word in phrases such as ‘I knew the man who did something’ and ‘He said that he would die’ seem to vary between sydd , a’, oedd and nothing. Help!! Gareth King’s Intermediate Welsh and SSIW Level 1 Challenges14 & 15 add up to more confusion!
Ok, so for who/which joining words in the middle of a sentence then…
If the second half of the sentence would use the present tense if it was on its own ( eg dw i, mae fe/o, yn ni) use ‘sydd’ - often shortened to ‘sy’ - which is a special word just for this purpose and must be there. You can use ‘yn’ or ‘wedi’ after sydd - for ‘ing’ or ‘has’ type sentences.
If the second half is any other tense, in theory ‘a’ is used to join the two halves - except in normal conversation in tends to be dropped. You will see it in writing and may hear it if someone is speaking very formally.
For ‘that’, there is a fairly similar situation in that if the second half of the sentence is present tense then ‘bod’ is used for ‘that’ - which must be there.
For any other tense in theory ‘y’ is used for that but is often dropped in normal speech.
Does that make sense?
Bear in mind, Nefyn, that - as Rich neatly summarises - those two examples you give there are different types of clause - the first is a relative clause, and the second is a that-clause - i.e. reported speech.
Relative clauses use a (SM) before the verb, unless the verb is mae, in which case you use sydd (because you’re not allowed to say a mae).
That-clauses never use a (or indeed sydd) - they use y or bod/fod (etc).
And both a and y can be dropped in speech - that’s what gives you your ‘nothing’ !
It’s a minefield out there!
So,to recap, “I met someone who wanted…” should be “nes i gyfarfod rhywun a oedd isio…” but in speech the a is dropped? But if I want to say “I met someone who is a Welshman” it can be “Nes i gyfarfod rhywun sy mae Cymro “ OK?
In your first one there, a oedd isio is correct.
In your second one, sy mae is wrong (you can never say sy mae) - sy is quite enough on its own, it includes both the who and the is: nes i gyfarfod â rhywun sy’n Gymro.