Sometimes in English it's possible to say a sentence that is perfectly correct in terms of grammar, but doesn't mean quite what you intended. So, why not try this quiz - it could save you some misunderstandings in future!
A quick language quiz (with answers):
1) You walk up to someone and say 'What's the problem?' What are they likely to do in response?
2) You walk up to someone and say 'What's your problem?' What are they likely to do in response?
3) You're talking about your job, and you say 'I work like an accountant'. Are you a qualified accountant?
4) You're talking about your job, and you say 'I work as an accountant'. Are you a qualified accountant?
5) Your friend says she's going on holiday for three days. When does she leave?
6) Your friend says she's going on holiday in three days. When does she leave?
Questions 1 and 2
1: They tell you what their problem is.
2: They punch you in the face (possibly).
In the first situation, you have asked the person what's wrong. Maybe they are upset, or stressed, and you want to help them. Assuming that they are happy for you to know (!), they are going to tell you why they're upset. A doctor might ask this question at the start of an appointment, and the patient would respond by describing their symptoms.
The tone of your second question is quite aggressive. Maybe you're in a pub, and a stranger has been staring at you, or behaving in another way that you find offensive or disagreeable. The question you are asking is 'What is your problem with me? Why are you acting like this towards me?' Be careful! You might not like how they respond. (Hmm, maybe don't try this one!)
The key here is that 'as' indicates what you are, while 'like' is used for similarity. 'I work like an accountant' means that you do a similar job to an accountant, but you aren't actually qualified as one. Maybe your job is difficult to explain so you're comparing it to an accountant's job to help your listener understand.
To help you remember the difference, the following sentence might be helpful:
'I work like a slave'.
The person saying this feels that they are under a lot of pressure, don't get paid enough, and (probably) aren't appreciated by their boss - it's a metaphor. What they are not saying is that they work for criminals without being paid, and are locked in a room every night!
5. She hasn't said.
6. If today is Wednesday, she is going on Saturday. (If today is Thursday, she is going on Sunday, and so on).
'In 3 days' refers to a specific point in the future, counting forward from the present. 'For 3 days' is talking about the length of time during which something happens - so in sentence 5 your friend is saying that there will be a continuous period of time during which she will be away from home.
In the past, this distinction doesn't apply: 'I haven't slept in three days' and 'I haven't slept for three days' mean the same thing
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