Oath vs Promise

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

Oath

Formal Top 3,000 (common) B1 noun

Promise

Top 1,000 (very common) A2 verb

Most formal: Oath Most common: Promise

	Oath	Promise
Pronunciation	🇬🇧 //əʊθ// 🇺🇸 //oʊθ//	🇬🇧 /["/ˈprɒmɪs/","/ˈprɒmɪsɪz/","/ˈprɒmɪst/","/ˈprɒmɪsɪŋ/"]/ 🇺🇸 /["/ˈprɑːmɪs/","/ˈprɑːmɪsɪz/","/ˈprɑːmɪst/","/ˈprɑːmɪsɪŋ/"]/
Meaning	A promise to tell the truth or do something important.	A commitment to do something or not do something.
Example	He took an oath to uphold the law.	I promise to help you with your homework.
Register	Formal	Neutral
How common	Top 3,000 (common)	Top 1,000 (very common)
CEFR level	B1	A2
Part of speech	noun	verb
Collocations	take an oath, sworn oath, oath of office, oath of allegiance	faithfully, solemnly, initially, can, cannot, seem to, to, as promised, I can’t promise anything
Antonyms	lie, dishonesty	lie, break, betray
Common mistakes	Confusing 'oath' with 'oaths' as the plural form., Using it in informal settings when it's typically formal.	Confusing 'promise' with 'vow' or 'pledge' in terms of strength., Using 'promise' without an object (e.g., 'I promise' should specify what)., Misusing in the past tense (e.g., 'I promised' without a follow-up).
Usage notes	Used in legal and ceremonial contexts. It may not be appropriate in casual conversation.	Use 'promise' when you want to express a vow or assurance. Common in both spoken and written contexts, but avoid in formal legal documents.

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

And one system shows promise.

and I always try to keep my promise.

And one system shows promise.

and I always try to keep my promise.

Promise

Frequently asked questions: Oath vs Promise

What's the difference between Oath and Promise?

Oath: A promise to tell the truth or do something important. Promise: A commitment to do something or not do something.

Which is more formal: Oath and Promise?

Oath is the most formal of these.

Which is more common: Oath and Promise?

Promise is the most common in everyday English.

Which is more advanced: Oath and Promise?

Oath is the highest level, at B1, on the CEFR scale.

Are Oath and Promise the same CEFR level?

Oath: B1, Promise: A2 on the CEFR scale.

What part of speech are Oath and Promise?

Oath: noun, Promise: verb.

Can you show an example of each?

Oath: He took an oath to uphold the law. Promise: I promise to help you with your homework.

Can I use Oath and Promise interchangeably?

Not always. Oath and Promise 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.