It has been shown that ... / What matters is ... (C1 Grammar)

Meaning: this keeps a long that-idea out of the subject slot — English prefers heavy information last, so the sentence opens lightly and lands on the weight. Form: put It at the front, then the verb (often a passive past participle: has been shown, is argued, is doubtful), then the that-part: "That exercise improves memory has been shown" becomes "It has been shown that exercise improves memory." Register: this is the standard, formal shape of academic and report writing — reach for it when a front-loaded That... subject would read as heavy or stilted.

Start with It, push the heavy part to the end

• That regular exercise helps has been shown. → It has been shown that regular exercise helps.
• That the results hold in every case is doubtful. → It is doubtful that the results hold in every case.
• That early action matters is widely agreed. → It is widely agreed that early action matters.
• Not "That exercise improves memory has been shown." — say "It has been shown that exercise improves memory.". Put It first and push the that-part to the end: easier to read.
• Try it: That the data supports the theory has been demonstrated. Start with It and push the that-part to the end. (Leave out the word you don't need.) Answer: It has been demonstrated that the data supports the theory. — Starting with It and moving the that-part to the end gives It has been demonstrated that the data supports the theory. "That the data" at the front is the heavy-subject version this move replaces, so it is left out. It holds the place while the heavy part waits until the end.

The same with a to + verb part

Meaning: the same end-weight move for a heavy to + base-verb idea — hold it back so the sentence opens lightly. Form: It + be + an adjective (essential, important, difficult) + to + base verb: "To consider every variable is essential" becomes "It is essential to consider every variable." Register: standard in careful, formal writing; the fronted To consider...is version sounds stiff, so lead with It and let the to-part close the sentence.

• To consider every variable is essential. → It is essential to consider every variable.
• To replicate the study will be difficult. → It will be difficult to replicate the study.
• To meet the deadline now will be hard. → It will now be hard to meet the deadline.
• Not "To consider every variable is essential before deciding." — say "It is essential to consider every variable before deciding.". Lead with It, then push the to + verb part to the end.
• Try it: To verify each source is important. Start with It and push the to + verb part to the end. (Leave out the word you don't need.) Answer: It is important to verify each source before publishing. — Leading with It and moving the to + verb part to the end gives It is important to verify each source before publishing. The long "to verify each source is" front version is what this move replaces, so it is left out. It holds the place at the start.

What ... is ... — hold the point back for emphasis

Meaning: a what-cleft splits a sentence in two so one part gets the spotlight. The What-half is treated as ground both sides already accept, and whatever follows is lands as the news. Form: What + a known clause + is/was + the focus: "The evidence suggests early action is critical" repackages as "What the evidence suggests is that early action is critical." The single linking is is essential; keep it singular to agree with the What-part, although with a plural focus you will also hear "What we need are more nurses". Register: an emphatic, rhetorical move for speech and formal writing alike — reach for it when you want to frame the point rather than merely state it. Note the mirror version, Innovation is what will decide this, which puts the focus first instead: same two parts, and you choose which end carries the weight.

• The evidence suggests early action is critical. → What the evidence suggests is that early action is critical.
• We need more time. → What we need is more time.
• The report really shows a funding gap. → What the report really shows is a funding gap.
• Not "What the evidence suggests early action is critical." — say "What the evidence suggests is that early action is critical.". Keep the linking is between the What-part and the focus — don't drop it.
• Try it: The evidence suggests that early action is critical. Build the version that holds the idea back for emphasis: What ... is ... (Leave out the word you don't need.) Answer: What the evidence suggests is that early action is critical. — This pattern builds up to the point: What the evidence suggests is that early action is critical. The link is a single is, so the doubled "is is" is left out. What + the known part holds the idea back, then is delivers the focus.

It was X that ... — spotlight who did it

Meaning: this picks out ONE element as the answer to an unspoken "which one?", and most often that element is the doer. Form: It + was / is + the spotlighted phrase + that + the rest of the sentence, unchanged: "The research team completed the report" becomes "It was the research team that completed the report." The spotlight implies a contrast — the team, not anyone else — so use it when the identity is the point. Note that who is possible for people ("It was Camila who signed it"), but that works for everything and is the safer default. Register: neutral to formal; common in reports, journalism and any writing that corrects or pins down a fact.

• The research team completed the final report. → It was the research team that completed the final report.
• Camila signed the authorisation. → It was Camila who signed the authorisation.
• The second audit uncovered the discrepancy. → It was the second audit that uncovered the discrepancy.
• Try it: You want to make clear that the DISTRIBUTOR, and no one else, canceled the order. Which sentence does that? (It was the distributor that canceled the order. / What the distributor did was cancel the order. / It was the order that the distributor canceled.) Answer: It was the distributor that canceled the order. — Putting the distributor in the spotlight slot is what says "this party, not another". The second option spotlights the ACTION (what they did was cancel), and the third spotlights the THING canceled — both are well-formed, but neither answers "which party?"

Never / Rarely / Seldom at the front — then the swap

You already met this swap under Not until: front the expression, then put the main clause into question order. A negative or near-negative adverb does the same thing. Meaning: fronting Never, Rarely, Seldom or Little makes the statement emphatic and formal. Form: the adverb + the helper + the subject + the base verb: "We never imagined this" becomes "Never did we imagine this." With a sentence that already carries a helper, move that one instead and no did appears ("Never have I seen such a response"). Little is the idiomatic one and always means the person was unaware: "Little did she know the meeting had been moved." Register: formal and literary — in ordinary speech you would simply say "I've never seen anything like it."

• We never imagined we would achieve this. → Never did we imagine we would achieve this.
• I have rarely seen such a clear result. → Rarely have I seen such a clear result.
• She did not know the meeting had moved. → Little did she know the meeting had moved.
• Try it: Which sentence fronts the negative adverb correctly? (Seldom does the committee overturn its own ruling. / Seldom the committee does overturn its own ruling. / Seldom overturns the committee its own ruling.) Answer: Seldom does the committee overturn its own ruling. — After the fronted adverb the helper comes first, then the subject, then the base verb: does the committee overturn. The second option leaves the clause in statement order with does merely inserted, and the third moves the main verb in front of its own subject, which is not the pattern — only the helper moves.
• Try it: Several factors have already been listed. Now the writer wants to single one out and put the spotlight on it: of everything mentioned, funding is the deciding factor. Which one spotlights the point rather than just stating it? (What decides the outcome is funding. / It has been shown that funding decides the outcome.) Answer: What decides the outcome is funding. — The writer wants to stress one factor above the rest, and the what-cleft holds the focus back to the end for exactly that emphasis: What decides the outcome is funding. "It has been shown that..." is the neutral, end-weight packaging — it reports the fact plainly but adds no spotlight, so it misses the emphasis the scene calls for. Read the two as a scale: extraposition = neutral, what-cleft = emphatic.