Sorry, but I'm on mobile. Why is it nil instead of ní?
If you're early on in the course (as I assume you are), it's best to just think of níl as the negative form of tá.
Thanks you! But why sometimes we have to use "ní" (ex: Ní maith liom beoir) and in this case we have to use "níl"? Is because of "ní" is the copular form of "níl" ?
Yes, ní is the copula (and the normal negative particle). Níl is only used for the negative of tá and is actually a contraction of ní fhuil (the same fuil that appears in an bhfuil)
Níl madra agam, tri madraí agam.