I know we can use both of them, but what is the exact explanation? Thank you 
Hi,
āto be in hospitalā means one is sick and currently under the hospitalās medical care.
āto be in the hospitalā means one, for whatever reasons, is in the hospital building. It may be the doctors or nurses working for the hospital.
āHeās in hospitalā and āHeās in the hospitalā both mean that he is in a hospital for examination and/or treatment.
āHe was hit by a car and now heās in hospitalā would tend to suggest that he is in there for some time while heās recovering (for however long that takes).
āHe was hit by a car and now heās in the hospitalā could mean the same, but is more likely to be used when he has been taken to hospital for a check-up, or possibly he will be there overnight and be released the next day.
āin hospitalā is longer term than āin the hospitalā which is either known to be temporary or, at least, not yet known to be long-term.
As Atomos pointed out, āHe is in the hospitalā could also be used as a reply to āWhere is the doctor?ā (in the same way as you could say āHeās in the houseā) but a more likely is āHeās at workā or āHeās at the hospitalā.
Actually, what you said is not entirely true
āIn hospitalā is used in British English and āin the hospitalā - in American English.
I know that to American, only āin the hospitalā sounds natural. (hopefully someone from the US can weigh in on this one).
The British and Canadians say āin hospitalā. The Americans say āin the hospitalā. If a person is only visiting the hospital or is there on an outpatient basis, Americans say he is āat the hospitalā.
My explanation is based on Michael Swanās Practical English Usage. It says you use āin hospitalā when youāre there as a patient, and āin the hospitalā when youāre there for other reasons. He also gives two examples.
āJaneās in hospital.ā (as a patient)
āI left my coat in the hospital when I was visiting Jane.ā
And yes, he also says that in American English, only āin the hospitalā is acceptable.
Itās not that āin the hospitalā is acceptable in American English, itās the only way to say it. āIn hospitalā sounds downright weird to American ears. The only reason it sounds okay to me is that in my city we see a lot of Canadian TV.
In the UK:
in hospital - staying in hospital as a patient.
in the hospital - visiting, working, receiving treatment (including staying as a patient, though not so likely to be used in that sense).
From a Canadian/American perspective, āin hospitalā definitely sounds British.
āIn the hospitalā is used in the US and in Canada. Some people might say āin hospitalā in Canada but most use āin the hospitalā - or at least my generation does.
I got it Thank you very much, everybody.
Iām another North American whoās lived several years in many states and want to āweigh inā on this for fun.
I have never heard āin hospitalā from anyone other than someone from outside the country.
All the Americans Iāve known say āin the hospitalā for being in the hospital for care. Adding the note above about being āat the hospitalā was a welcome note, too. Iād not thought of the distinction before seeing this post.
An article points to a singular noun.
I was happy to see the British definition, too, because I correspond with friends who use the British rules. Now I know why I see they omit the article so often.
I grew up watching TV coming from Windsor and Toronto, and the news anchors and TV announcers always said āin hospitalā, as far as I can remember. I wonder if they were adhering to a British standard that people donāt use on the street.
By the way, Linda, what do you call a sweet, fizzy drink like Coca-Cola or 7 Up?
Pampers, we use the same rules in the US also, but just not with āhospitalā. We say āin prisonā but āat the prisonā. āIn schoolā but āat the schoolā (among other things). So itās not a British-only rule; we just have an exception in the US with āhospitalā.
Hi Jamie,
I canāt remember if news reporters use āin hospitalā in Canada (probably) but I donāt and neither do the people I know. I grew up in western Canada but Iāve lived in the US for the past six years.
As for fizzy, sweet drinks: I say āpopā but my American husband says āsoda.ā haha
In England we call a sweet, fizzy drink a fizzy drink
My experiences are obviously not the same as Gzornenplatās.
In general, people use the brand names of well-known brands (7 Up, etc.), ācokeā when referring to cola-based drinks of pretty much any variety, ālemonadeā. If using a more general expression then āpopā is the usual term. Very rarely would anyone actually refer to it as a āfizzy drinkā.
The reason I asked Linda about the āfizzy drinkā is that the terminology varies in the US, and I wanted to see what someone from western Canada would say.
If you look at the dialect maps of the US, the majority of the land mass is āpopā country, some parts of the South call everything a ācokeā, no matter what flavor it is, and āsodaā is concentrated on parts of the two coasts and in Chicago. However, people who have moved to New York, Chicago or LA, or have moved from there, think theyāre more worldly when they reject the term āpopā and start saying āsodaā. Many of them actually look down on people who say āpopā.
Advertisers used to avoid this dialect difference by calling everything a āsoft drinkā, but over the past 10 years or so they have started aggressively using the word āsodaā.
I live in ācoke landā.
In the UK 'sodaāis most commonly considered to be soda water (water which has been carbonated).
Itās exactly the same in the US Midwest.