why
why — adverb
1. used when you want to know the cause, purpose, or explanation of an action, even
used when you want to know the cause, purpose, or explanation of an action, event, or situation — asking what made something happen or what someone's intention was.
Why did Eitan decide to move back to Japan after living in London for ten years?
direct question: why + did + subject + verb
Reema asked her brother why he had not called their mother on her birthday.
reported question: asked + why + subject + verb (normal order)
Why is the library closed on Sunday when so many students want to study there?
Jiwoo could not understand why her application for the scholarship was rejected.
Think our new recycling policy is unfair? Tell me why instead of just shrugging.
- how come
informal equivalent used in casual conversation; does not require auxiliary inversion ('How come you left?')
- for what purpose
more formal and specific about intention rather than general cause
文法句型
why + do/does/did + subject + verb?
why + be + subject?
reported: ask/wonder/know + why + subject + verb
用法筆記
In everyday spoken English, 'why' is very frequently used alone as a one-word question after a statement (e.g. 'I am not going.' 'Why?'). It also pairs with 'not' to make suggestions: 'Why not try the new café?'
常見錯誤
why — conjunction
1. introduces a clause that gives the cause or purpose of an event, explaining what
introduces a clause that gives the cause or purpose of an event, explaining what made it happen or what someone intended — used after verbs like 'know', 'explain', 'understand', and 'ask'.
Christopher explained why he had missed the team meeting — his flight was delayed by six hours.
explain + why + clause (past perfect)
That is why Kenji always checks the oil level before a long drive.
that is why + clause (result structure)
Do you see why Amihan was upset when the school moved her daughter's flute lesson from Tuesday to Saturday morning?
The teacher showed the class why water expands when it freezes.
Nobody could figure out why the printer kept jamming every time they used blue paper.
- for which reason
more formal; often used in academic or legal writing
- the reason that
interchangeable in most contexts, though 'the reason that' is slightly more explicit
文法句型
know/understand/explain/see + why + clause
that is why + clause
the reason is why + clause
用法筆記
When 'why' introduces an embedded clause (after 'know', 'explain', 'wonder', etc.), the clause keeps normal subject-verb word order — do not use the inverted question structure. Compare: 'Why did she leave?' (direct question) vs. 'I know why she left.' (embedded clause).
常見錯誤
2. used after a noun such as 'reason' or 'cause' to link it to a clause that explai
used after a noun such as 'reason' or 'cause' to link it to a clause that explains the content of that reason — for example, 'the reason why they left' means 'the reason for which they left'.
The main reason why Élise moved to Berlin was the opportunity to work in film.
the reason why + clause
There are several reasons why the old bridge needs to be replaced before winter.
The contractor listed the main reasons why the roof replacement took longer than planned.
Can you think of any reason why the bank should not approve Mr. Kim's loan application for the new restaurant?
One reason why Justin enjoys teaching is that he loves watching students discover new ideas.
- for which
the formal equivalent; 'the reason for which they left' is more formal and less common in speech
文法句型
the reason why + clause
the reasons why + clause
(a/the) cause why + clause
用法筆記
Some traditional style guides discourage 'the reason why' as redundant ('reason' already contains the idea of 'why'), but this construction is extremely common in both spoken and written English at all levels, and most modern dictionaries accept it as standard. Removing 'why' ('the reason they left') produces a cleaner style that is also correct.
常見錯誤
why — exclamation
1. said at the beginning of a sentence to show that you are surprised, mildly annoy
said at the beginning of a sentence to show that you are surprised, mildly annoyed, or have just suddenly understood something that you had not noticed before.
Why, if it is not young Cyrus! I hardly recognised you with that beard.
surprise at recognising someone
Why, that was exactly what Dr. Nakamura told me to do — take a short walk every hour.
Why, I have been waiting for this bus for almost forty minutes — this is ridiculous!
Why, I never expected to find Hiro at a tango festival — he told me he hated dancing.
文法句型
Why, + full sentence
Why, + fragment (noun phrase)
用法筆記
This exclamation is heard less often in modern everyday speech than in older English or in literature. Younger speakers are more likely to use 'Oh!' or 'Hey!' to express the same feeling. However, it remains common in some regional varieties of English and in formal writing meant to sound dramatic or old-fashioned.
常見錯誤
why — noun
1. the causes, explanations, or reasoning that lie behind an action, decision, or s
the causes, explanations, or reasoning that lie behind an action, decision, or situation — appearing almost always as part of the set phrase whys and wherefores, which refers to the full set of reasons and background details.
The report explained all the whys and wherefores of the company's decision to close three factories.
fixed phrase: the whys and wherefores [+ of]
Before you criticise the new hospital budget, learn the whys and wherefores behind each cut.
Zola did not care about the whys and wherefores — she just wanted the problem fixed by Friday.
Before the company holiday party, Emre wanted to understand the why behind each sudden rule change the HR team announced.
文法句型
the whys and wherefores of + noun phrase
the why behind + noun phrase
用法筆記
The plural expression 'the whys and wherefores' is by far the most common form of this noun sense. Using 'why' as a standalone countable noun ('the why behind something') is a more recent, informal development often seen in business and self-development writing.