Formal vs. Informal English: When to Use Which (With Examples)
One of the trickiest things about English is knowing when to sound professional and when to sound relaxed. Use formal English in a casual Slack message and you sound robotic. Use informal English in a client email and you sound unprofessional.
Native speakers switch between formal and informal English instinctively. they read the room and adjust. As a non-native speaker, you can learn to do the same thing. It just takes understanding the patterns.
What Makes English Formal or Informal?
The difference comes down to a few key areas:
Vocabulary: Formal English uses longer, Latin-based words. Informal English uses shorter, Germanic-based words.
- Formal: "We need to ascertain the cause." / Informal: "We need to figure out the cause."
- Formal: "I would like to inquire about..." / Informal: "I wanted to ask about..."
- Formal: "Please commence the project." / Informal: "Let's start the project."
Sentence structure: Formal English uses complete sentences, passive voice, and complex structures. Informal English uses fragments, contractions, and simple structures.
- Formal: "The report has been completed and will be distributed this afternoon."
- Informal: "Done with the report. I'll send it around this afternoon."
Tone: Formal English is distant and impersonal. Informal English is warm and direct.
Side-by-Side Comparisons
Greetings
| Formal | Informal |
|--------|----------|
| Dear Mr. Thompson, | Hey James, |
| Good morning, Ms. Rivera. | Morning, Sofia! |
| It is a pleasure to meet you. | Great to meet you! |
| I hope this message finds you well. | Hope you're doing well! |
| How do you do? | How's it going? |
Making Requests
| Formal | Informal |
|--------|----------|
| I would appreciate it if you could send me the report. | Could you send me the report? |
| Would it be possible to reschedule our meeting? | Can we move our meeting? |
| I was wondering if you might be available on Tuesday. | Are you free Tuesday? |
| I would be grateful for your assistance with this matter. | Could you help me out with this? |
| Please do not hesitate to contact me. | Just let me know. |
Expressing Opinions
| Formal | Informal |
|--------|----------|
| I believe this approach has significant merit. | I think this is a great idea. |
| In my view, we should reconsider the timeline. | I think we should push back the deadline. |
| I would respectfully disagree with that assessment. | I don't think that's quite right. |
| It is my understanding that the budget has been approved. | From what I heard, the budget's been approved. |
| I am of the opinion that further research is needed. | I feel like we need to look into this more. |
Apologizing
| Formal | Informal |
|--------|----------|
| I sincerely apologize for the inconvenience. | Sorry about that! |
| Please accept my apologies for the delay. | Sorry for the late reply. |
| I regret to inform you that we are unable to proceed. | Unfortunately, we can't move forward with this. |
| I take full responsibility for the oversight. | My mistake. I'll fix it. |
Emails
Formal email (to a client you have not met):
"Dear Ms. Chen,
Thank you for your inquiry regarding our consulting services. I would be happy to schedule a call at your convenience to discuss your requirements in greater detail. Please find attached our service overview for your reference.
I look forward to hearing from you.
Kind regards,
David"
Informal email (to a colleague you work with daily):
"Hey Li,
Thanks for flagging this. I'll take a look this afternoon and get back to you. Quick question. is this urgent or can it wait until Monday?
Cheers,
David"
Same person, same language skills, completely different register. Both are correct. in their respective contexts.
How to Read the Room
So how do you know which register to use? Here are your clues:
Go more formal when:
- You are writing to someone for the first time.
- You are communicating with a client, customer, or senior executive.
- The situation is serious (complaints, legal matters, formal requests).
- You are writing a document that will be widely shared (reports, proposals, official communications).
- You are unsure when in doubt, err on the side of formality. You can always relax later.
Go more informal when:
- You know the person well and communicate regularly.
- The channel is casual (Slack, Teams chat, WhatsApp).
- Your team culture is relaxed (common in tech startups, creative agencies).
- The other person uses informal language first. match their level.
- You are in a social situation (lunch, coffee, team events).
The escalation rule: Start formal with a new contact and gradually become less formal as the relationship develops. Let the other person set the pace. If they sign their email "Best regards, Jonathan," do not reply with "Thanks, Jon!". at least not yet.
Register Switching: The Advanced Skill
The most impressive thing a non-native speaker can do is switch registers smoothly depending on context. Here is what that looks like:
In a board presentation: "Based on our analysis, we recommend proceeding with Option A, which is projected to yield a 20% improvement in operational efficiency."
In a team standup (30 minutes later): "So basically, we're going with Option A. It should save us about 20% on operations. I'll share the details in Slack."
In a message to a colleague (5 minutes later): "Hey, we got the green light on Option A. Can you start on the implementation plan?"
Same information, three different registers, all appropriate for their context.
Common Mistakes Non-Native Speakers Make
Being too formal in casual settings:
Writing "Dear Colleague, I hope this email finds you well. I am writing to inform you that the meeting room is booked" in a Slack message to a teammate will get you teased. "Hey, meeting room's booked" is all you need.
Being too informal in formal settings:
Sending "Hey, wanna hop on a call? Thx" to a prospective client you have never met is too casual. "Hi Ms. Rodriguez, would you have time for a brief call this week? I'd love to discuss how we might work together."
Mixing registers in the same message:
"Dear Sir, just wanted to touch base real quick about the aforementioned contractual obligations. Cheers!" Pick one register and stick with it.
Using slang you do not fully understand:
Informal English is full of slang that changes meaning in different contexts. If you are not sure about a word, stick with standard informal language. "That's great" is always safe. "That slaps" might confuse half your audience.
A Simple Framework
When you are about to write or speak, ask yourself two questions:
1. Who is my audience? (Boss, client, close colleague, stranger)
2. What is the channel? (Formal email, Slack message, in-person meeting, casual chat)
The answers will tell you which register to use. Over time, this becomes automatic, just like it is for native speakers.
Master register switching in practice
Our Professional English Basics course teaches you how to communicate confidently in every work situation, from formal presentations to casual Slack conversations.
For email-specific guidance, Writing in English covers the full spectrum from formal client emails to quick internal messages.
Grab our free formal/informal phrase guide. a side-by-side reference sheet you can keep open while writing.