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'Buy' means to purchase something; 'by' is the preposition for proximity, authorship, or deadline.
Side-by-side comparison
"Buy" is the verb to purchase. "I need to buy milk" = I need to purchase milk. Its past tense is "bought".
I need to buy a new laptop before the project starts.
She bought three months of advertising space online.
Can you buy some coffee on your way to the office?
"By" is a preposition with many uses: agent in the passive ("written by"), proximity ("by the door"), means ("by car"), deadline ("by Friday").
Please submit the form by five o'clock today.
The novel was written by a first-time author.
She sat by the window reading the contract.
Common mistake
"We need to by new supplies" (correct: buy) and "Buy the time she arrived" (correct: By the time) are fast-typing errors caused by the identical sound of both words.
Trick to remember it
- •"Buy" has a U for "use money", you use money to buy.
- •"By" has no U and is the multi-purpose preposition: location, authorship, means, or deadline.
Quick rule
- •"Buy" = to acquire with money (verb).
- •"By" = preposition of location, means, authorship, or deadline ("by Friday", "by car", "by the author").
Did you know?
The idiom "buy time" (to deliberately delay something to gain more time) has nothing to do with money, time is treated metaphorically as a commodity you can purchase. This ancient metaphor exists in many languages and is reinforced by "time is money", if time has monetary value, then logically you can "buy" it. A small word, "buy", with a surprisingly large metaphorical life.
Practise what you learned
Exercise 1 · Pick the right one
She sat _____ the window and watched the rain.
Exercise 2 · Pick the right one
I need to _____ a new charger. Mine broke yesterday.
Exercise 3 · Form the word
Related word pairs
One means to receive or agree to something, the other means to exclude or not include.
'Advice' is the guidance you receive (noun); 'advise' is the act of giving that guidance (verb).
'Affect' is the verb meaning to influence something; 'effect' is the noun meaning result or consequence.
'Aisle' is the walkway between rows of seats or shelves; 'isle' is a small island.
Bryan López
Founder of SpeakUP Academy