development and regular occurrence
4.122 To show that something develops gradually, or happens at regular intervals, you can use a general time word with by followed by the same general time word.
She was getting older year by year, and lonelier, and more ridiculous.
Millions of citizens follow, day by day, the unfolding of the drama.
Gradual development can also be indicated by the adverbs increasingly and progressively.
…the computers and information banks on which our world will increasingly depend.
His conduct became increasingly eccentric.
As disposable income rises, people become progressively less concerned with price.
Talking about how long something lasts
4.123 The following section explains ways of showing how long something lasts or takes.
Some adverbs and adverbial expressions are used to show how long an event or state lasts. Here is a list of adverbs that are used to show duration:
always
briefly
forever
indefinitely
long
overnight
permanently
temporarily
She glanced briefly at Lucas Simmonds.
You won’t live forever.
The gates are kept permanently closed.
Briefly and permanently can be used in the comparative.
This new revelation had much the same outward effect, though more briefly.
This is something I would like to do more permanently.
The form long is only used as an adverb in negatives and questions.
I haven’t been in England long.
How long does it take on the train?
In affirmative clauses, it is used in expressions such as a long time and prepositional phrases such as for a long time. However, the comparative and superlative forms longer and longest can be used in affirmative and negative clauses.
Then of course you’ll go with Parry. She’s been your friend longer.
I’ve been thinking about it a lot longer than you.
She remained the longest.
In affirmative and negative if-clauses, you can use for long.
If she’s away for long we won’t be able to wait.
prepositional phrases
4.124 However, prepositional phrases are more commonly used. The following prepositions are used in adverbials of duration:
after
before
for
from
in
since
throughout
to
until
The prepositional object can be a noun phrase referring to a specific period of time. This can be in the singular after the determiner a (or one for emphasis), or in the plural after a number or quantity expression.
The noun phrase can also refer to an indefinite period, for example expressions such as a long time, a short while, a while, or ages, or plural time words such as hours.
for for length of time
4.125 The preposition for indicates how long something continues to happen.
Is he still thinking of going away to Italy for a month?
The initial battle continued for an hour.
This precious happy time lasted for a month or two.
For the next week, she did not contact him.
We were married for fifteen years.
I didn’t speak for a long time.
She would have liked to sit for a while and think.
You use the instead of a when the period of time is already known, with seasons, periods of the day, and weekend, or when you modify the time word with words like past, coming, following, next, last, or an ordinal.
Tell Aunt Elizabeth you’re off for the day.
We’ve been living together for the past year.
For the first month or two I was bullied constantly.
For the next few days he had to stay in bed.
Put them in cold storage for the winter.
I said I’m off to Brighton for the weekend.
Remember that you do not use a determiner with special periods of the year.
At least come for Christmas.
4.126 For can also be used with specific time adverbials to show the time when something is to be used, not how long it takes or lasts.
Everything was placed exactly where I wanted it for the morning.
4.127 For can also be used in negative statements when you want to say that something need not or will not happen until a certain period of time has passed. Yet is often added.
It won’t be ready to sail for another three weeks.
I don’t have to decide for a month yet.
for for emphasis
4.128 For is used with a plural noun phrase to emphasize how long something lasts.
Settlers have been coming here for centuries.
I don’t think he’s practised much for years.
I’ve been asking you about these doors for months.
4.129 You can also use a general time word with after followed by the same general time word to emphasize that a state continues for a long time or that an action is repeated continuously for a long time.
I wondered what kept her in Paris decade after decade.
They can go on making losses, year after year, without fearing that they will go bust.
in and within for end of a period
4.130 In is used to indicate that something happens or will happen before the end of a certain period of time. In more formal English within is used.
Can we get to the airport in an hour?
That coat must have cost you more than I earn in a year.
The face of a city can change completely in a year.