What is plain English and why does it matter?
Plain English is writing designed so the intended reader can understand it the first time, at the speed they normally read. It is not simplified English, not dumbing down, and not short words for their own sake — it is writing that puts the reader's comprehension ahead of the writer's convenience.
What it involves in practice:
Everyday words where they exist. Use rather than utilise, buy rather than purchase, about rather than with regard to. Technical terms stay where they are the precise word; jargon goes where it is habit.
Active voice with a visible actor. "We will refund you" beats "a refund will be issued", because the passive version conceals who does it — sometimes deliberately.
Shorter sentences, one idea each. Long sentences are not wrong, but a document averaging 40 words per sentence is hard work regardless of vocabulary.
Direct address. You and we rather than the applicant and the Authority.
Structure that helps. Informative headings, lists for lists, the important thing first.
Why it matters:
It is a fairness issue. Adult literacy surveys in the UK and US consistently find a substantial proportion of adults struggle with complex prose. Documents that decide people's benefits, healthcare, tenancy or legal position are exactly the documents most likely to be written impenetrably.
It is legally required in places. The US Plain Writing Act 2010 mandates it for federal agencies. UK and EU consumer regulations require contract terms to be in plain, intelligible language, and ambiguity is generally construed against the drafter.
It reduces cost. Organisations that rewrite forms and letters plainly consistently report fewer support calls and fewer errors.
The common objection — that plain English loses precision — usually gets it backwards. Vagueness hides in complexity; plain writing exposes where the meaning was never settled.