"Can I add sugar in/to milk?" Which preposition is correct?

Question

I want to say "Can I add sugar in/to milk?" Should I use "in" or "to"?

Answer 1

You should use "add to" when the sentence specifies what is receiving the sugar and "add in" (or just "add") when it doesn't. Compare

I have a glass of milk. Can I add sugar to it?

vs

I have a glass of milk. Can I add in sugar?

Answer 2

"Can I add sugar to milk?" would be correct.

Answer 3

If you are holding a mug of milk and adding sugar to it for taste then you will use the preposition to

In this case you might also change the sentence slightly to read:

Can I add sugar to **my milk?**

Using the position to in this context makes sense because to is functioning to show a transfer from person to place. (from you to the mug of milk). The use of in or into would only suggest position and lack the idea of transfer or movement.

I hope that helps.

Some help from: The Ins and Outs of Prepositions By Jean Yates Ph.D.