Across
We useacrossas a preposition (prep) and an adverb (adv).Acrossmeans on the other side of something, or from one side to the other of something which has sides or limits such as a city, road or river:
We took a boat[PREP]acrossthe river.
[PREP]Acrossthe room, she could see some old friends. She got up and went to join them.
My neighbour came[ADV]acrossto see me this morning to complain about our cat.
The road was so busy that we found it difficult to get[ADV]across.
We also useacrosswhen something touches or stretches from one side to another:
The Ponte Vecchio is a beautiful old bridgeacrossthe river Arno in Florence.
She divided the page by drawing a red lineacrossit. Then she cut it in two.
Especially in American English,across fromis used to refer to people or objects being ‘opposite’ or ‘on the other side’:
The pharmacy isacross fromthe Town Hall.
Helen’s office is justacross frommine.
We useacrossto emphasise that something is happening at the same time in many places, e.g. within an organisation, a city or a country:
She’s opened coffee shopsacrossthe city and they’re very successful.
Acrossthe country, people are coming out to vote for a new president.
We also useacrossto refer to the width or diagonal measurement of something:
The size of a television screen is measured from the higher corner of one side to the lower corner of the other side, that is, from one corneracrossto the opposite corner.
Acrosscomes after measurements when we talk about diameter or width:
The building is 157 metres long, 92 metresacrossand the façade is 68 metres wide.
Over
We useoveras a preposition and an adverb to refer to something at a higher position than something else, sometimes involving movement from one side to another:
From the castle tower, you can see[PREP]overthe whole city.
We toasted marshmallows[PREP]overthe fire.
We drove high up[PREP]overthe mountains on a narrow dangerous road.
Suddenly a plane flew[ADV]overand dropped hundreds of leaflets.
Come overoften means to come to the speaker’s home:
You mustcome[ADV]overand have dinner with us some time.
Especially when we use them as adverbs,overcan mean the same asacross:
We walkedoverto the shop.(orWe walkedacrossto the shop –the shop is on the other side of the road)
I was goingacrossto say hello when I realised that I couldn’t remember his name.(orI was goingoverto say …meaning ‘to the other side of the street or room’)
Acrossorthrough?
Movement
When we talk about movement from one side to another but ‘in something’, such as long grass or a forest, we usethroughinstead ofacross:
I love walkingthroughthe forest.(throughstresses being in the forest as I walk)
Not:I love walking across the forest.
When my dog runsthroughlong grass, it’s difficult to find him.(throughstresses that the dog is in the grass)
Not:When my dog runs across long grass…
Time
When referring to a period of time from start to finish, American English speakers often usethroughwhere British English speakers sayfrom … to/till …:
The office is open MondaythroughFriday, 9 am–5 pm.(preferred British form:from Monday to Friday)
We useover, notthrough, to refer to periods of time from start to finish when a number is specified (of days, weeks, etc.):
Overthe last few days, I have been thinking a lot about quitting my job.
Across,overandthrough: typical errors
When moving from one side to another while surrounded by something, we usethroughnotacross:
We cycledthrougha number of small villages.
Not:We cycled across a number of small villages.
When we talk about something extending or moving from one side to another, we useacrossnoton:
The papers were spreadacrossthe table.
Not:The papers were spread on the table.
We don’t usethroughwhen we’re talking about periods of time from start to finish and we mention a specific number of days, weeks, etc:
We haven’t seen each other muchoverthe last four years.
Not:We haven’t seen each other much through the last four years.