Formal vs Informal Words: Complete Reference

Formal vs Informal Words: Complete Reference

Introduction — why this vocabulary matters

Choosing the right words—formal or informal—affects how your message is received. Knowing the difference between formal vs informal words helps you match tone to context, whether you're writing a business email, a college essay, or a casual text to a friend.

This guide gives a practical, categorized word list, short example sentences, usage tips, and quick exercises so you can apply these choices immediately. If you want to rewrite or test your sentences, try Rephrasely’s AI writer and Composer to experiment with tone adjustments: Rephrasely Composer.

Categorized Word List

Below are common formal–informal pairs organized by theme. Each list item highlights the pair; use the short notes to decide when to use each.

• Greetings & Closings
  • Good morning / Hello — Formal vs informal greeting for different audiences.
  • Sincerely / Best — Formal closing vs casual email sign-off.
• Requests & Permissions
  • Request / Ask — "Request" suits formal documents; "ask" is everyday speech.
  • Permission / Okay — "Permission" is formal/legal; "okay" is casual approval.
• Responses & Reactions
  • Affirmative / Yes — "Affirmative" or "indeed" can sound formal or emphatic.
  • Negative / No — Straightforward, but tone varies by word choice (e.g., "not at this time").
• Reasons & Explanations
  • Because / Since / As — "Because" is neutral; "since" and "as" are more formal when introducing explanations.
  • Due to / Because of — "Due to" reads more formal, often used in academic or professional writing.
• Help & Assistance
  • Assist / Help — "Assist" fits professional contexts; "help" works everywhere.
  • Provide assistance / Give a hand — One formal, one informal.
• Start & Finish
  • Commence / Begin / Start — "Commence" is formal; "start" and "begin" are neutral.
  • Terminate / End / Finish — "Terminate" is formal and strong; "end" is neutral; "finish" is casual.
• Need & Requirement
  • Require / Need — "Require" is formal and often used in policies.
  • Necessary / Needed — "Necessary" is slightly more formal.
• Purchase & Possession
  • Purchase / Buy — "Purchase" appears in contracts and formal writing.
  • Obtain / Get — "Obtain" is formal; "get" is informal.
• Communication
  • Inform / Tell / Notify — "Inform" and "notify" are formal; "tell" is everyday.
  • Respond / Reply — "Respond" tends to sound more formal than "reply" in some contexts.
• Manners & Politeness
  • Apologize / Sorry — "Apologize" is formal and explicit; "sorry" is casual and common.
  • Accept / Take up — "Accept" is formal when agreeing to offers.

Example Sentences

Here are concise examples for key formal/informal pairs. Use them to mimic tone in your writing.

• Purchase — Buy

  Formal: I intend to purchase the necessary equipment next quarter.

  Informal: I'm going to buy some new equipment next week.

• Require — Need

  Formal: This position requires a master's degree in the relevant field.

  Informal: You need a master's for this job.

• Assist — Help

  Formal: Our team will assist you in completing the registration process.

  Informal: We’ll help you sign up.

• Notify — Tell

  Formal: Please notify the office of any schedule changes in writing.

  Informal: Tell the office if your plans change.

• Commence — Begin

  Formal: The program will commence on July 1.

  Informal: The program starts on July 1.

• Apologize — Sorry

  Formal: I apologize for the delay in responding to your message.

  Informal: Sorry I didn't get back to you sooner.

• Obtain — Get

  Formal: You must obtain approval before proceeding.

  Informal: You need to get approval first.

• Terminate — End / Finish

  Formal: The contract may be terminated with a 30-day notice.

  Informal: The contract can end with 30 days' notice.

Usage Tips — when to use formal vs casual alternatives

Match your word choice to audience, purpose, and medium. Formal words work best in legal documents, academic papers, and professional emails. Informal words are appropriate for texts, quick emails, social media, and conversations.

Keep these actionable rules in mind:

• Tip 1: If you’re unsure, aim for neutral language—words like "begin," "help," and "inform" are safe and widely accepted.
• Tip 2: In emails, mirror the other person's tone. If they write "Hi" and "Thanks," you can keep it informal.
• Tip 3: Avoid overly formal words that sound pompous (e.g., "hereinafter") unless the context demands legal precision.
• Tip 4: Use formal words to be precise; use informal words to be personable and clear.

To practice rewriting sentences from formal to informal (or vice versa), use Rephrasely Composer or the AI writer to generate tone variations. After rewriting, check originality with the plagiarism checker and verify whether the text looks AI-written with the AI detector. If a piece reads too robotic, try the humanizer tool for natural phrasing.

Practice Exercises

Complete these short exercises to test your understanding. Answers are below.

1. Fill in the blank (formal or informal): "Please ______ me of any updates by Friday." (options: notify, tell)
2. Choose the better formal word for a job posting: "Applicants must ______ a cover letter." (options: submit, send)
3. Match the pairs: 1) Buy — a) Purchase; 2) Help — b) Assist; 3) Tell — c) Inform
4. Rewrite this informal sentence into a formal one: "Can you help me get the report by Monday?"

Answers

• 1 — notify
• 2 — submit (both work, but "submit" is more formal)
• 3 — 1a, 2b, 3c
• 4 — Formal rewrite: "Could you assist me in obtaining the report by Monday?"

Frequently Asked Questions

How do I know when to use formal vs informal words?

Consider audience and purpose. Use formal words in academic, legal, or professional contexts and informal words for friends, social media, and casual messages. When unsure, choose neutral vocabulary and mirror the tone of your recipient.

Can I mix formal and informal words in the same document?

Mixing tones can be acceptable if done intentionally—for example, a semi-formal newsletter may use friendly language but still maintain professional terms. Avoid abrupt tone shifts within a single paragraph; keep sections consistent.

What tools help me practice tone and wording?

Rephrasely’s Composer and AI writer can rewrite text in different tones, while the plagiarism checker, AI detector, and humanizer help ensure originality and naturalness. Use them to iterate until your tone matches your intent.