Student or Learner
As a rule of thumb, can one state that when using a positive statement one has to use the words "someone" and "something", while questions and negative statements go with "anyone" and "anything", although there are exceptions in which words are interchangeable like in "Did you see something/anything ?" ?
As a very general rule, yes.
Oh no, I spilled my drink.
1. Question: Do you have anything to mop it up with?
2. Negative Statement: No, I"m sorry I don't have anything.
3. Positive statement: Darn. I just need something quick... anything!
4. Positive statement: Oh, here's something you can use.
1. This could be something, but anything sounds better to me.
2. Something doesn't really work here.
3. Notice that both work here - the second one is a plea for "any darn thing!"
4. Anything would NOT work here.
Try another dialog and let's see how interchangeable they are.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.