Introduces an established fact or historical truth.

Signals credibility by indicating the information is well‑known among experts or generally recognized.

When providing background context at the start of academic texts, reports, or scholarly articles; when citing long‑standing knowledge.

Academic writing (research papers, essays), professional documents (technical reports, policy briefs), and formal presentations where authority matters.

It has long been known that

It has long been known that

The clause after 'that' can be any factual statement, proposition, or clause describing a widely accepted truth.

• that
• the dangers
• the importance
• the link

• It has been established that
• There is a long tradition of
• Researchers have long known

'It has long been known about' – using ‘about’ instead of simply stating the fact.

"It is common knowledge that" (less formal)

Learners may default to active voice or omit passive construction entirely, missing this academic convention.

• established fact openers

Conveys an authoritative tone and sets up subsequent claims by anchoring them in historically accepted information.

Signals erudition and builds trust with readers familiar with scholarly conventions.

‘long known’ = something widely recognized for ages

This chunk is used to introduce well-established facts in academic and professional contexts, emphasizing the long-standing nature of the knowledge.

from "We know" → "It is known that" → "It has long been known that"