Does the sentence "I'm at work" simply and exactly mean "I am working now", or it has a slight difference in meaning? Whether "at" has anything to do with the work place, or it's simply refering to working itself?
This is a great question. For years, it confused me so I suspect you come from a similar situation. I will use my personal experience to explain, and trust my example can be extrapolated to other demographics.
The exact meaning of those words depends on:
- who is saying it,
- where they work, and
- the proximity of their home to their work.
I grew up and lived on the farm till age forty; now I live in the city. I learned that the same words and phrases regarding "work" have different meanings for farm folk than they do in urban society. They may have yet different meanings for other demographics, but this answer will examine how "work" is spoken of on the farm and in urban society in North America.
Since my search for understanding began on the family farm, I will begin my explanation with farm definitions. Let us acknowledge that language means what speakers make it mean. In other words, just because urban dwellers far outnumber farm folk in North America, they don't get to define the language of farmers.
On the family farm, where work and play happens in the same place with the same people, "I am working now" means that "I am not playing or fooling around. I am contributing to the production of food for the family and money for the farm and bank account." After a break or meal, farm folk might push back their chairs from the table and say, "I'd better get back to work," meaning to clear the table and wash the dishes, then continue whatever tasks needed doing about the farm. For city folk, that might seem like "chores around the house." For farm folk it's work because "I am working right now."
In my own hometown in Ontario, people say "I'm at work," when they mean that they are at their place of work.
"I'm Working" means "I have a job."
I'm working also means:
What you see me doing is paid work. I may be on the road or appear to be chatting or playing a video game, but this is part of what I'm paid to do.
"Being at Work"
Normally, when people people say, "I'm at work," their exact meaning is that they are at their place of work. Even if they are on break they will say, "I'm at work."
That is what I, as a farmgirl, used to find confusing. How could a person who was sitting in the breakroom chatting and sipping coffee claim to be working?
ANSWER: They were at their workplace. Thus, they were at work though possibly not "hard at work" at the moment.
These people have a home that is not at the same place as their work. If they "take work home," or if they do their work with a computer or telephone that is at home, they might say, "I'm working from home."
Farmers don't "work from home"; they just work. I can see this kind of culture clash occur in other demographics, too, with regards to "work" references. That's what makes this such a great question.
The examples of the postal worker and teacher were added to the question after I started writing. I did not see them until after posting my answer. I think I touched on that kind of situation indirectly.
It would mean you are at the place where you do work.
And by "work" I mean "employment" and not "study".
A person like a postman might say they are at work when they are walking the streets delivering the mail.
A person who works from home is not likely to say that they are "at work". A teacher is not "at work" if he is at home marking books, although he can be ‘hard at work’.
People at work may not necessarily be working. If they are not working at work, they are available to be visited or to visit somewhere else, or to receive something/someone at their workplace. In this case, "I'm at work" already assumes they are not working, and is only a matter of location.
On the other hand, people at work may be working. This is why I would add a qualifier to "being at work" to distinguish it from physical location when I'm actually working at work: "I'm hard at work", "I'm busy at work", "I'm stuck at work". "I'm working" or "I'm busy" also works. :P
Context and tone is also super important. If someone knows me well, they might know that I'm usually "working" at work, in which case it's enough for me to say "I'm at work". Or if I say "I'm at work" in an abrupt and negating tone, that means I am busy working at work. If they know I'm usually not working at work, then I am saying "I'm at work" to imply that I'm available.
Confusingly, I myself do work from home, but I will say "I'm at work" if someone doesn't know that I work from home, for convenience and to tell them I'm unavailable. Most people automatically assume "I'm at work" means "I am working", hence I'm unavailable. I would not say "I'm at work" if I'm working from home but am available to be elsewhere. In this case I'd simply say, "I'm at home" because I am not working. On the other hand, if I am unavailable because I am working, I will say "I am working from home", but location doesn't really matter at this point so "I am working" also suffices.
Use this to be ultra clear:
At work At home Working "I'm working at work" "I'm working at/from home" Not working "I'm not working at work" "I'm not working at/from home"
This is less clear but is still correct:
At work At home Working "I'm at work" "I'm working" Not working "I'm not working" "I'm home"
This seems to be the confusing part:
At work At home Working "I'm at work"** "I'm at work" Not working "I'm at work"<< "I'm home"
Pointed by <<, context and tone are important, and location matters immediately after. "I'm at work, so I'm 10 minutes away". "I'm at work, so meet me in the lobby". By **, context, tone, is important, but location no longer matters and hence is said abruptly. Most people assume **, i.e. that usually people are working at work.
I can see how all of this is confusing! Especially because people can say "I'm working" even when they are not currently working, but they are speaking more generally and will not clarify it if it's obvious they are not physically, presently doing work. Sadly, they will also say "Right now, I'm working" or "Currently, I'm working" or "I work" even when physically, presently, currently, and right now they are not working. They just mean they have a job.