uncountable nouns

Question

normally we use "de" for make uncountable words negative

for example je ne vois pas de lait

but what do we have to in these sentences?

"je ne peux pas boire de lait" or je ne peux pas boire du lait
which one is correct

ı wish your helps.. Merci beaucoup

Answer

Je ne peux pas boire de lait. -- I can't drink milk.
If you said, "Je ne peux pas boire du lait," that sounds like "I can't drink the milk" to French ears.

Answer

ok but  why don't we  use  "Je ne peux pas boire le lait," i nstead of  "Je ne peux pas boire du lait"because "Le" is  a  definite artcticle.

Answer

If you want to say that you cant drink milk in general as, e.g., you are lactose intolerant, then you say je ne peux pas boire de lait. In a literal sense it means: I cannot drink of milk.

Remember, this is a language and not math. You may be able to come up with some rule only to learn later that it doesn't apply in general. To add to your confusion, if you want to say that you hate milk, you say je déteste le lait. Here, suddenly, the definite article is used to connote the general.