Formal English vs Informal English: When to Use Each

The same idea can sound completely different depending on how you say it. “I was wondering if you could possibly send over the report” and “Can you send the report?” mean the same thing, but they land very differently depending on who you’re speaking to. Choosing the right register, formal or informal, is one of the most useful and most overlooked skills in English, and it’s something even advanced learners get wrong regularly.

What actually separates formal from informal English

Formal and informal English differ in four main ways: contractions, vocabulary, sentence length and directness. Formal English spells out contractions (do not instead of don’t), prefers single-word Latinate verbs over phrasal verbs (investigate instead of look into), uses longer, more complete sentences, and softens requests with extra words. Informal English does the opposite on every count: contractions, phrasal verbs, shorter sentences, and direct requests. Neither is “better” English. They’re different tools for different situations, and using the wrong one in the wrong place is what actually damages how you come across.

Side-by-side comparison

Where each register belongs

Use formal English with people you don’t know well, senior colleagues, clients, official emails, cover letters and any written communication that represents your company. Use informal English with close colleagues, friends, casual messages and everyday conversation. The tricky zone is everything in between, a colleague you know but who’s more senior, a client you’ve worked with for years, a professional group chat. In that zone, start more formal and let the other person set the tone; it’s much easier to relax your language later than to recover from starting too casually.

Formal English in emails

Email is where register mistakes show up most often, because the wrong tone is preserved in writing and easy to reread. A few habits make written English sound more formal without sounding stiff or old-fashioned: open with “Dear” rather than “Hi” for a first message to someone senior, spell out contractions, use “I would like to” instead of “I want to,” and close with “Kind regards” or “Best regards” rather than “Cheers” or “Thanks.”

Phrasal verbs: the biggest informal signal

Phrasal verbs (look into, put off, come up with, get back to) are some of the most common and most informal features of English. Native speakers use them constantly in everyday speech, but in formal writing, they’re often swapped for a single-word equivalent. This doesn’t mean phrasal verbs are wrong in formal settings, spoken formal English still uses many of them, but written formal English generally prefers the single-word alternative. Learning a handful of common swaps (look into → investigate, put off → postpone, come up with → devise, get back to → respond to) instantly raises the formality of your writing.

Common mistakes with register

Two mistakes come up again and again. The first is being too formal in casual settings, which can sound cold or distant to colleagues you actually know well. The second, more common among learners preparing for professional English, is being too informal in formal settings: opening a client email with “Hey,” using slang in a cover letter, or texting a manager the way you’d text a friend. When in doubt, lean slightly more formal. It’s a much smaller social cost than being seen as careless or overly casual in a professional context.

Frequently Asked Questions

Formal and informal English are both correct, they simply belong in different places. Learn the small vocabulary and structure swaps that shift the tone, pay attention to how your relationship with the listener changes over time, and you’ll find yourself switching between the two almost without thinking about it.