Oath vs Swear

When to use each in English, with meaning, register, and examples.

Oath

Formal Top 3,000 (common) B1 noun

Swear

Informal Top 2,000 (common) B2 verb

Most formal: Oath Most common: Swear

	Oath	Swear
Pronunciation	🇬🇧 //əʊθ// 🇺🇸 //oʊθ//	🇬🇧 /["/sweə(r)/","/sweəz/","/swɔː(r)/","/swɔːn/","/ˈsweərɪŋ/"]/ 🇺🇸 /["/swer/","/swerz/","/swɔːr/","/swɔːrn/","/ˈswerɪŋ/"]/
Meaning	A promise to tell the truth or do something important.	To use rude or offensive words.
Example	He took an oath to uphold the law.	I swear to tell the truth in my testimony.
Register	Formal	Informal
How common	Top 3,000 (common)	Top 2,000 (common)
CEFR level	B1	B2
Part of speech	noun	verb
Collocations	take an oath, sworn oath, oath of office, oath of allegiance	loudly, quietly, silently, hear somebody, at, solemnly, on oath, under oath, be prepared to, make somebody, by, on, to, be sworn into office, swear somebody to secrecy, swear somebody to silence, solemnly, on oath, under oath, be prepared to, make somebody, by, on, to, be sworn into office, swear somebody to secrecy, swear somebody to silence, solemnly, on oath, under oath, be prepared to, make somebody, by, on, to, be sworn into office, swear somebody to secrecy, swear somebody to silence, solemnly, on oath, under oath, be prepared to, make somebody, by, on, to, be sworn into office, swear somebody to secrecy, swear somebody to silence
Antonyms	lie, dishonesty	praise, compliment
Common mistakes	Confusing 'oath' with 'oaths' as the plural form., Using it in informal settings when it's typically formal.	Confusing 'swear' with 'promise' — they have different meanings., Using it in formal writing where it's not acceptable., Using 'swear to' instead of 'swear at' when expressing anger.
Usage notes	Used in legal and ceremonial contexts. It may not be appropriate in casual conversation.	Used in informal settings to express anger or frustration. Often considered inappropriate in formal contexts. Be cautious of the audience and setting before using.

See it in real clips

Game Of Thrones › S1 E1

He swore an oath, Cat.

Game Of Thrones › S1 E1

You swore the king an oath, my lord.

Those people sat on the stand under oath.

Game Of Thrones › S1 E1

He swore an oath, Cat.

Game Of Thrones › S1 E1

You swore the king an oath, my lord.

Oath

I swear. All the guineas are buying it, huh?

How I Met Your Mother › S1 E1

- I swear. - I swear.

I swear. All the guineas are buying it, huh?

How I Met Your Mother › S1 E1

- I swear. - I swear.

Swear

Frequently asked questions: Oath vs Swear

What's the difference between Oath and Swear?

Oath: A promise to tell the truth or do something important. Swear: To use rude or offensive words.

Which is more formal: Oath and Swear?

Oath is the most formal of these.

Which is more common: Oath and Swear?

Swear is the most common in everyday English.

Which is more advanced: Oath and Swear?

Swear is the highest level, at B2, on the CEFR scale.

Are Oath and Swear the same CEFR level?

Oath: B1, Swear: B2 on the CEFR scale.

What part of speech are Oath and Swear?

Oath: noun, Swear: verb.

Can you show an example of each?

Oath: He took an oath to uphold the law. Swear: I swear to tell the truth in my testimony.

Can I use Oath and Swear interchangeably?

Not always. Oath and Swear are related and overlap in some contexts, but they differ in register, how common they are, and usage, so swapping one for another can change the meaning or tone. Check the differences above before substituting.