Every sentence has one part that matters most. Maybe it was the timing, not the plan, that caused the problem. Maybe you need the blue file, not the red one. In speech you can stress a word with your voice, but in writing — and in careful speaking — English uses a grammar tool instead: the cleft sentence. 'It was the timing that caused the problem.' 'What I need is the blue file.' Clefts put a spotlight on exactly one piece of information.

Without clefts, your corrections and explanations can sound flat or unclear. Compare 'The timing caused the problem' with 'It wasn't the plan — it was the timing that caused the problem.' The second one settles an argument. Clefts are everywhere in meetings, emails, and everyday disagreements, so they are worth mastering.

A cleft sentence 'cleaves' — splits — one simple sentence into two parts so that one part gets the focus. Start with a plain sentence: 'Anna fixed the printer on Monday.' You can highlight almost any piece of it, depending on the question you are answering.

The it-cleft has the form: It + be + FOCUS + that/who + the rest. To highlight the person: 'It was Anna who fixed the printer.' To highlight the thing: 'It was the printer that Anna fixed.' To highlight the time: 'It was on Monday that Anna fixed the printer.' The verb 'be' matches the tense of the story — 'It was...' for past events, 'It is...' for present facts. Use 'who' for people and 'that' for almost everything else.

The wh-cleft (also called a pseudo-cleft) starts with a 'what' clause: What + clause + be + FOCUS. 'What Anna fixed was the printer.' 'What I need is more time.' This shape saves the new information for the end, which is where English likes to put surprises. It is very common in speech: 'What worries me is the cost.' You can also reverse it: 'The cost is what worries me.'

A useful cousin uses 'do' to focus on the action itself: 'What she did was (to) restart the router.' And for things and people, 'the thing / the one' work like 'what': 'The thing I love about this cafe is the bread.' 'The one who called was your sister.'

How do you choose? Use an it-cleft to correct or contrast: 'It was Tom, not Jerry, who broke the cup.' Use a wh-cleft to introduce your main point smoothly: 'What we should discuss first is the budget.' Both mean the same as the plain sentence — they only change what shines. One structural warning: after the focus, the rest of the original sentence follows in normal order. Do not shuffle the leftover words.

1. 1. It was my neighbor who found the lost cat.

   The it-cleft highlights the person; 'who' introduces the rest.

2. 2. It was the salt that ruined the soup, not the pepper.

   An it-cleft used to correct a wrong idea.

3. 3. It was in Osaka that we first tried real ramen.

   You can focus a place phrase, keeping 'that' afterwards.

4. 4. It was only last night that the fever finally dropped.

   A time expression in focus; the verb 'was' matches the past story.

5. 5. Was it the manager who approved the refund?

   It-clefts can become questions: 'Was it... who...?'

6. 6. It isn't money that makes this job hard.

   A negative it-cleft: 'It isn't X that...' denies the focus.

7. 7. What I need right now is a strong coffee.

   A wh-cleft: the 'what' clause first, the focus at the end.

8. 8. What annoys me is the noise from the street.

   'What' + verb of feeling is a very common spoken pattern.

9. 9. What she did was call the airline immediately.

   The 'what... did was' shape focuses on the whole action.

10. 10. What matters most is that everyone arrives safely.

    The focus after 'is' can be a whole 'that' clause.

11. 11. The thing I like about winter is the quiet.

    'The thing... is' works like a wh-cleft for things.

12. 12. The one who booked the tickets was my brother.

    'The one who' focuses a person, like 'what' does for things.

13. 13. A hot shower is what I want after that hike.

    A reversed wh-cleft: focus first, 'what' clause second.

14. 14. It's the small shops that give this street its charm.

    Present-tense it-cleft ('It's') for a general fact.

The first mistake is scrambling the leftover clause, like the error 'It was caused the problem the timing.' A cleft has a fixed skeleton: It + be + focus + that + normal clause. Pick the focus ('the timing'), put it right after 'was', then let the rest follow in ordinary order: 'It was the timing that caused the problem.' If your sentence has two verbs fighting each other after 'was', the skeleton is broken.

The second mistake is forgetting 'that' or 'who' entirely: 'It was the timing caused the problem.' In careful English you need the connector: '...the timing that caused the problem.' Similarly, learners sometimes write 'What I need is I need more time', repeating the verb. The 'what' clause already contains 'I need', so the part after 'is' holds only the focus: 'What I need is more time.'

A third mistake is agreement in wh-clefts. The 'what' clause counts as singular, so use 'is', even when the focus is plural: 'What we need is more chairs', not 'What we need are more chairs' in everyday style. Also match 'be' to the story's time: 'It WAS the timing that CAUSED...' — past with past.

• It-cleft skeleton: It + be + focus + that/who + rest (normal order).
• Use 'who' for people, 'that' for things, times, and places.
• Wh-cleft saves the news for the end: 'What I need is X.'
• To correct someone, prefer an it-cleft: 'It was X, not Y, that...'.
• Do not repeat the verb after 'is' in a wh-cleft.
• Match the tense: 'It was... that happened', 'It is... that matters'.