Alli di ddim vs Dwyt ti ddim

I came across these two sentences today that have me a bit confused.

You can’t go to bed and You can’t drive

They were translated respectively as

Alli di ddim mynd i’r gwely and Dwyt ti ddim yn gallu gyrru

Is there a difference in meaning between them Alli di ddim and Dwyt ti ddim or are they interchangeable in these sentences?

These are two ways of conjugating in Welsh. The first uses a direct conjugation of the verb gallu, whereas the second uses a conjugation of bod followed by gallu.

So the two bits you have highlighted are not the same until you add the verb in the second one -
Alli di ddim = you can’t (you are not able)
Dwyt ti ddim = you are not
Dwyt ti ddim yn gallu = you can’t (you are not able)


Diolch yn fawr iawn Siaron. Dw i’n deall.