"Nac oes, does dim rhaid symud."
Translation:No, there is no need to move.
Would does dim angen symud be the same, or would it have a different shade of meaning?
A sentence I came across more than once is "there is no need to go now", which accepts both does dim angen mynd nawr and does dim eisiau mynd nawr.
So I wonder whether rhaid , angen and eisiau are interchangeable for "need", or should be chosen according to the context.
"Rhaid" is a "must" or "necessity". So "Mae rhaid i mi fynd." is "I must go". "Angen" is a "need" so "Dw i angen mynd" is "I need to go". "Eisiau" is a "want" and sometimes a "need". So "Dw i eisiau mynd" is almost always going to be interpreted as "I want to go". Whilst "To need to" and "To must" (and "To have to") often have overlapping conotations it is best to translate them to "Angen" and "Rhaid i" respectively.
@EllisVaughan's explanation and advice is good. It can get confusing when you put words like eisiau and angen in different constructions. There is some overlap, but broadly:
"Jac wants to go"
Mae Jac eisiau mynd
Mae Jac yn moyn mynd
Mae Jac am fynd (This can also mean "Jac intends to go", especially in the north)
"Jac needs to go"
Mae Jac angen mynd
Mae angen i Jac fynd
Mae eisiau i Jac fynd
"Jac must go" / "Jac has to go"
Rhaid i Jac fynd
Mae Jac yn gorfod mynd
By the way, just one more question.
Is rhaid ever used as a verb, i.e. bod + pronoun + yn rhaid?
According to the App Geiriaduron rhaid is a noun-verb, but in these sample constructions it is the only one always used as a noun.
I'm just curious about this.
I think Ap Geiriaduron / Geiriadur Bangor has made the mistake because it's taken English infintives, "must" and "necessitate", and made the link: English infinitive = Welsh verbnoun. This works for almost every case (English infinitive "run" = Welsh verbnoun "rhedeg") but not with rhaid, which Geiriadur Prifysgol Cymru lists as only a noun (or an adjective). It's undoubtedly a machine rather than human error.
You do have the (usually more formal) option of yn before rhaid in:
Mae'n rhaid i Jac fynd
lit. "It is a necessity that Jac goes"
as an alternative to the more usual:
Mae rhaid i Jac fynd
lit. "There is a necessity that Jac goes"
But you can never say:
*Mae Jac yn rhaid mynd
lit. "Jac is a necessity go" :(
"Does" is the negative form of "mae" and here expresses "There is not" (in conjunction with "dim"). EDIT: "Does" is used as opposed to "Dydy/Dyw" because the object is indefinite.