B1–B2

At-Phrases and For-Phrases — English Grammar Exercises

by mistake, on time, in advance — get the preposition right every time

At-Phrases and For-Phrases in English

'At' and 'for' both form a rich set of fixed adverbial phrases. These two prepositions are grouped together in this subtopic because several of their phrases involve near-confusables ('at first' vs 'in first', 'for free' vs 'in free'). Frequency data from the British National Corpus places 'at least', 'at once', 'for free', and 'for good' among the most common fixed prepositional adverbials in everyday English.

Core At-Phrases

at least — There were at least fifty people at the concert.
at once — The doctor said she needs to rest at once. (= immediately)
at first — At first, I didn't like the city, but now I love it.

Core For-Phrases

for free — The museum is open for free on Sundays.
for good — She's left the company for good. (= permanently, forever)
for sale — Is this house for sale? (= available to buy)

'At First' vs 'In the End'

These two phrases often appear together to describe a change over time: 'At first I was nervous, but in the end everything went well.' Note: 'in first' and 'at the end' (without 'of') are both incorrect in this usage.

Common Mistakes

✗ You should book in least two weeks ahead. → ✓ You should book at least two weeks ahead.
✗ In first, I didn't like the city. → ✓ At first, I didn't like the city.
✗ She's left for good. → ✓ She's left for good. (This one is correct — 'for good' uses 'for'.)

Frequently Asked Questions

What is the difference between 'on time' and 'in time'?

'On time' means punctual — at the exact scheduled moment: 'The train arrived on time.' 'In time' means not too late — with enough time to spare, often implying it was a close call: 'We arrived in time to catch the last train.' A useful test: if you can replace the phrase with 'punctually', use 'on time'. If you can replace it with 'just in time' or 'before it was too late', use 'in time'.

What is the difference between 'for sale' and 'on sale'?

'For sale' means available to buy at its normal price: 'Is this house for sale?' 'On sale' means available at a reduced, discounted price: 'Winter coats are on sale — 40% off.' In British English, 'on sale' can also simply mean 'available in shops', but in the context of a discount, both British and American English use 'on sale'.

Why do we say 'by mistake' but 'on purpose'?

These are fixed idiomatic expressions with no logical rule — they must be learned as units. 'By mistake' and 'by accident' both describe unintentional actions ('by' here expresses manner or means). 'On purpose' describes intentional action ('on' here is part of a fixed set phrase). Speakers of Russian often confuse these because the Russian phrase «по ошибке» (by mistake) and «намеренно» (on purpose) do not map onto English prepositions predictably.

What is the difference between 'at the end' and 'in the end'?

'At the end' requires 'of' and refers to the final point of a specific, identifiable thing: 'At the end of the film, everyone cried.' 'In the end' means eventually or after a long process of deliberation — no 'of' follows: 'In the end, we decided to stay home.' A simple test: if you can follow it with 'of [something]', use 'at'. If it means 'eventually' or 'after everything', use 'in'.