Formal and informal speech are different registers, meaning different choices of words, grammar, and tone depending on the situation. Formal speech is used when you need distance, respect, or professionalism. Informal speech is used when you want friendliness, ease, or closeness. Good communication is choosing the register that fits the relationship, setting, and purpose.

Use formal language in professional messages, academic writing, official requests, customer service, and when speaking to someone you do not know well. Use informal language with friends, family, close coworkers, and casual online chat. When unsure, start formal and soften later if the other person writes informally or invites a more relaxed tone.

Formal speech often sounds more polite because it uses respectful framing, indirect requests, and careful wording. Informal speech can still be polite, but it is usually more direct and relaxed. In English, politeness is often created through modal verbs, softeners, and respectful phrases rather than special verb forms.

Rule	Example
Use indirect requests to sound formal.	Could you please send the updated file by Friday?
Use modals to soften and stay polite.	Would you mind waiting a moment?
Use direct imperatives mainly in informal contexts.	Send me the file when you can.
Add softeners for friendly informality.	Just checking if you saw my message.

Formal English prefers precise, neutral, and sometimes Latinate vocabulary, while informal English prefers simpler, everyday words. The meaning may be similar, but the social effect changes: formal words create distance and professionalism; informal words create warmth and ease. Avoid slang, strong idioms, and texting shortcuts in formal contexts.

Word/Phrase	Definition	Example
purchase	buy in a formal way	We plan to purchase new equipment.
inquire	ask for information formally	I am writing to inquire about availability.
assist	help in a formal way	Our staff can assist you.
request	ask formally	I would like to request a refund.
kids	informal word for children	The kids are home from school.
info	informal short form of information	Thanks for the info.

Contractions like I’m, don’t, and we’ve are common in informal speech and make writing sound conversational. Formal writing often avoids contractions to sound more neutral and careful, especially in academic or official documents. In many workplace emails, contractions are acceptable if the overall tone is professional.

Rule	Example
Avoid contractions in very formal writing.	We do not have sufficient information at this time.
Use contractions for a friendly, natural tone.	We don’t have enough info yet.
Match the other person’s level of formality.	If they write I’m available, you can too.

Formal English tends to use longer, more structured sentences, clearer transitions, and full explanations. Informal English prefers shorter sentences, simpler connectors, and more implied context. Both can be clear; the difference is how much structure and explicitness you add.

Rule	Example
Use explicit transitions in formal writing.	Therefore, we recommend postponing the launch.
Use simpler connectors in informal writing.	So I think we should wait.
Prefer complete sentences in formal contexts.	I will review the document and respond tomorrow.
Fragments are common informally, especially in chat.	Sounds good. Tomorrow works.

Requests are a key place where register matters because they can sound demanding or respectful. Formal requests often use could, would, may, and polite openings like I was wondering if. Informal requests often use can, want, or a simple imperative, especially with friends.

Rule	Example
Use Could you or Would you in formal requests.	Would you be able to confirm receipt?
Use May I for very formal permission.	May I ask a quick question?
Use Can you in neutral to informal requests.	Can you send it today?
Use imperatives with close relationships.	Let me know when you’re free.

Openings and closings strongly signal formality in emails and letters. Formal greetings use Hello, Dear, or Good morning and often include titles and last names. Informal greetings use Hi and casual openings, and closings can be short or friendly. Choose a closing that matches the relationship and the seriousness of the message.

Word/Phrase	Definition	Example
Dear Ms. Patel	formal greeting with title and surname	Dear Ms. Patel,
Hello Dr. Chen	formal to neutral greeting	Hello Dr. Chen,
Hi Sam	informal friendly greeting	Hi Sam,
Sincerely	formal closing	Sincerely, Jordan Lee
Best regards	professional but less formal closing	Best regards, Jordan
Thanks	informal closing	Thanks, Jordan

Slang, strong idioms, and internet expressions create an informal voice and can confuse people who do not share the same background. In formal contexts, replace slang with clear literal language. In informal contexts, slang can build connection, but it can also sound unprofessional if the relationship is not close.

Rule	Example
Avoid slang in formal communication.	The plan is not feasible at this time.
Use literal language for clarity across audiences.	We need to reduce costs by 10 percent.
Use slang only with the right audience.	That meeting was pretty intense.

You can shift between formal and informal speech by changing a few high-impact signals: greeting, contractions, word choice, and request style. Softening or strengthening formality helps you manage relationship and authority without changing the message. Aim for consistency so the tone does not feel mixed or confusing.

Rule	Example
To become more formal, remove contractions and add polite modals.	Could you please review the report?
To become more informal, shorten and use everyday words.	Can you take a look at the report?
Keep formality consistent from greeting to closing.	Hello Ms. Rivera ... Best regards