prepositions - "In between" or "between"?

• There's a misunderstanding (in) between us.

Is it natural with in or without? In which case should we add in?

Answer

You can use in between when referring to something physical:

There is a puddle in between us.

But when referring to something intangible or metaphorical, stick with between:

There is some tension between us.

Note that, in the first case, the in is optional; one could just as well say:

There is a puddle between us.

However, the in reads awkwardly when talking about something more abstract, and should therefore be omitted:

We have a disagreement in between us.

_{Note: American English; other dialects may treat this differently}