By Who or By Whom: Which Is Correct in Modern English?

“By who” or “by whom” can look almost identical, but they follow different grammar patterns. If you have ever paused while writing a sentence such as “By who was this book written?” you are not alone. The confusion usually comes from knowing that who and whom refer to people but serve different grammatical roles.

The traditional grammar rule is simple: who is generally used as a subject, while whom is used as an object. Because the preposition by is followed by an object, “by whom” is traditionally considered the grammatically formal choice. For example, “By whom was the painting created?” follows the traditional rule.

However, everyday English is more flexible than formal grammar rules suggest. Native speakers frequently use “by who” in casual conversation, especially when the sentence sounds more natural that way. In this guide, you’ll learn when to use by who or by whom, why by whom is preferred in formal writing, and how modern English treats both expressions.

Quick Answer

“By whom” is the grammatically correct and standard form in formal English, while “by who” is informal and commonly used in spoken English.
“Whom” is the object form of “who,” and after prepositions like “by,” traditional grammar prefers “whom.” However, modern English often allows “who” in casual contexts.

Quick Comparison Table

Pronunciation Section

How Are These Words Pronounced?

• Who → /huː/
• Whom → /huːm/

Phrases:

• By who → /baɪ huː/
• By whom → /baɪ huːm/

Syllable Breakdown:

• who = 1 syllable
• whom = 1 syllable

👉 There is no major pronunciation difference, only a final nasal sound in “whom.”

Meaning and Usage

Meaning of “Who”

“Who” is a pronoun used as the subject of a sentence.

Examples:

• Who is calling you?
• Who made this cake?

In informal speech, people often extend it incorrectly into phrases like “by who.”

Meaning of “Whom”

“Whom” is the object form of “who”, traditionally used after prepositions like by, to, with, for.

Examples:

• By whom was this report written?
• To whom should I speak?
• With whom are you traveling?

Main Difference Between By Who or By Whom

👉 The key rule: After “by”, traditional grammar requires “whom.”

Grammar Rule Section

Why “Whom” Is Used After “By”

In English grammar:

• Who = subject
• Whom = object

Since “by” is a preposition, it needs an object after it.

Rule:

Preposition + object pronoun → “whom”

Example:

• Correct: By whom was the decision made?
• Incorrect: By who was the decision made?

Modern Grammar Reality

In modern English:

• “Whom” is slowly disappearing in spoken language
• Many native speakers use “who” in all contexts
• Formal writing still prefers “whom”

Origin and Etymology

The words come from Old English:

• Who → Old English hwā (meaning “what person”)
• Whom → Old English hwām / hwom (dative/object case)

Over time:

• English lost much of its case system
• “Whom” became less common in speech
• “Who” started replacing it informally

Dictionary Comparison

Oxford Dictionary

• Recognizes “whom” as formal object pronoun
• Notes “who” often replaces it in spoken English

Cambridge Dictionary

• Accepts “who” in informal contexts after prepositions
• Still marks “whom” as grammatically correct

Merriam-Webster

• States “whom” is formal or traditional
• Notes decline in everyday usage

Collins Dictionary

• Emphasizes modern shift toward “who” in conversation

👉 All dictionaries agree:

• “By whom” = formal standard
• “By who” = informal modern usage

Are Both Words Correct?

Yes — but context matters.

• By whom → grammatically correct (formal English)
• By who → acceptable in informal speech

👉 Neither is “wrong” in real-life usage, but one is more appropriate depending on context.

British vs American English

Which Form Is More Common?

• Spoken English: “by who” is more common
• Academic writing: “by whom” dominates
• News & journalism: mostly “by whom”
• Social media: “by who” widely used

👉 Trend: “whom” is declining, but still important in formal English.

When Should You Use Each Word?

Academic Writing

Use: by whom

• Essays
• Research papers
• Exams

Professional Writing

Use: by whom

• Emails
• Reports
• Business documents

Casual Writing

Use: by who

• Text messages
• Social media posts
• Informal chats

Journalism

Prefer: by whom

Common Mistakes

Mistake 1

❌ By who was this done?
✔ By whom was this done?
👉 Preposition requires object form.

Mistake 2

❌ Who was this letter written by? (informal confusion)
✔ By whom was this letter written?

Mistake 3

❌ By whom did you go with?
✔ Who did you go with? (modern acceptable alternative)

Real-Life Examples

• Formal: By whom was the project approved?
• Academic: By whom was this theory developed?
• Casual: By who did you talk to?
• Modern speech: Who did you go with?

Synonyms

For “Who”

• Which person
• What person

For “Whom”

• To whom (formal structure use cases)
• Object pronoun equivalents (him/her/them)

Antonyms

These pronouns do not have direct antonyms, but contrast forms include:

• Who ↔ Whom (subject vs object)
• He ↔ Him
• She ↔ Her

Memory Trick

👉 Replace “who” with “him” or “he”:

• If “him” fits → use whom
• If “he” fits → use who

Example:

• By him → By whom ✔
• By he → incorrect ❌

Similar Confusing Words

• Who vs Whom
• Who vs Whose
• Who vs That
• By vs With (preposition confusion)

Why Do People Search “By Who or By Whom”?

People search this keyword because:

• Grammar confusion in exams
• English learning doubts
• Writing formal emails
• AI grammar correction tools flagging sentences
• IELTS / TOEFL preparation

Common search queries:

• Is it by who or by whom correct?
• When to use whom after by?
• Difference between who and whom
• Is whom still used in English?

FAQs

1. Is “by who” correct?

Yes, in informal English, but not grammatically standard.

2. Is “by whom” always correct?

Yes, in formal and traditional grammar.

3. What is the main difference?

“Whom” is object form; “who” is subject form.

4. Which should I use in exams?

Always use by whom.

5. Is “whom” still used in 2026?

Yes, mainly in formal writing.

6. Do native speakers use “whom”?

Less in speech, more in writing.

7. Can I say “who” instead of “whom”?

Yes, in casual conversation.

8. Why is “whom” disappearing?

Because modern English simplifies grammar in speech.

9. Is “by who” wrong?

Not wrong informally, but not preferred in formal grammar.

10. What is the safest choice?

Use by whom in professional or academic contexts.

Expert Recommendation

Linguists and grammar editors agree:

• Use “by whom” in formal writing
• Use “who” in casual speech
• Avoid overusing “whom” in spoken English unless necessary

Style guides like APA and Chicago still prefer “whom” after prepositions.

Final Verdict

• Both forms exist
• “By whom” is grammatically standard
• “By who” is informal and conversational
• Choose based on context, not confusion

Key Takeaways

• “Who” = subject
• “Whom” = object
• After “by,” formal grammar prefers “whom”
• Modern English often simplifies to “who” in speech

Practical Advice

If unsure:
👉 Use “by whom” in writing
👉 Use “by who” only in casual conversation

Michael Patel

I’ve dedicated my career to making English grammar approachable for everyone. I know how intimidating grammar rules can feel, so I focus on practical examples and real-life applications that I personally use every day. My books, Grammar in Action and Clear Writing, Confident Speaking, reflect my hands-on approach to learning. When I’m not writing, I explore linguistic trends, and I’m always on the lookout for ways to make language fun and empowering for learners.