'At the office' refers generally to the state of someone who works in an office of some kind being at work, e.g.
"Where's Bob?", said Jim.
"At the office.", replied John
It can also refer to an object being at said place of work:
"Where's your briefcase?", said Jim.
"I left it at the office.", said John.
'In the office' refers to someone or something physically being in a specific office, e.g.
"Where's Bob?", said Jim. "In his office.", said John.
This would usually be used when the office in question was in close proximity to the speakers, for example if Jim and John were in another office in the same building as Bob.
"Where's the telephone?", said Jim. "It's in the office", said John.
However, in and at are often interchangeable. Take the briefcase example. John could have said:
"I left it in my office."
To summarise, 'at' is a more general, vague term, whereas 'in' usually refers to a specific location.
I don't think in your mind would be used as in your example. However we do say:
- Do you have anything in mind?
which means "What is it you are thinking of?" or "Do you have a preference/suggestion?"
Want to go out for lunch?
Sure. What do you have in mind?
How about that new Thai place?
in your mind is used to mean "in your imagination".
I swear, that guy is after me.
Oh relax, it's just in your mind.
And on your mind indicates worry or preoccupation.
You look worried. Do you have anything on your mind?
Best Answer
The way these different prepositions are used is all very much idiomatic, so there will be a limit to how far you can "rationalise" why any particular preposition is associated with any particular meaning. Especially in respect of "hand", since most of us always have a couple of those about our person ready to be incorporated into our word choices.
One thing I would say that "in" usually denotes something closer than "on" (which itself is usually closer than "at"), which is why the "nearby" meanings use the latter two.
Note that "in hand" doesn't actually mean having more time at your disposal - it's just that we often say we have "time in hand" (things in hand can be in reserve, spare). Apart from the literal held in the hand, the other common idiomatic usage for this one is that if something is "in hand" it's being actively dealt with (by implication, really close to you), not just sitting on your "to-do" list.
OP doesn't mention to hand, which is actually more common than the others in British English (but seemingly quite rare for Americans). In practice few would choose at hand or on hand on the basis of how physically close/accessible something was - largely pointless anyway, since few others would apprehend any subtle distinction being made. Go British and make life easier for everyone!