- denken aan = think of/think about, simply thinking about anything that crosses your mind
- denken over = thinking including having an opinion, this usually needs an adverb
- nadenken over = more deeply thinking about how something should be solved, how something should be, plans for the future, etc.
nadenken aan incorrect Dutch
ik denk aan de opdracht = I think about the assignment (simply thinking about the fact that you have this assignement)
- ik denk na over de opdracht = I think about how to complete the assignment
- ik denk aan haar = I think of her
- ik denk positief over haar = I think positively about her (about how she is)