yr hyn

What in questions and in statements. English uses "what" in two ways. In a question (What do you want?) Welsh says beth. When "what" means "the thing that", careful Welsh says yr hyn ('r hyn after a vowel): Dyna'r hyn dw i eisiau.

What follows yr hyn. Yr hyn works like a noun with a relative clause after it:

• as the subject of a present verb, use sy: yr hyn sy'n bwysig (what is important)
• with a short verb form, the verb softens: yr hyn ddwedodd hi (what she said); formal Welsh adds a: yr hyn a ddywedodd hi; see Relative A
• with bod: yr hyn dw i eisiau (what I want), yr hyn roedd e'n ei feddwl (what he was thinking)

At the front. Yr hyn often starts a sentence to point to the important part, followed by ydy (yw in the South and in writing): Yr hyn sy'n bwysig ydy dy iechyd (What matters is your health).

In speech. Relaxed speech often uses beth or be instead: Dyna be dw i isio (North), Dyna beth dw i eisiau. Yr hyn is usual in writing, on the news and in careful speech. Both are correct for their setting.

Hyn on its own means this: Mae hyn yn bwysig (This is important). See This and That.