I swear vs Promise

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

I swear

Informal Top 2,000 (common)

Promise

Top 1,000 (very common) A2 verb

Most formal: Promise Most common: Promise

	I swear	Promise
Pronunciation	🇬🇧 //aɪ swɛər// 🇺🇸 //aɪ swɛr//	🇬🇧 /["/ˈprɒmɪs/","/ˈprɒmɪsɪz/","/ˈprɒmɪst/","/ˈprɒmɪsɪŋ/"]/ 🇺🇸 /["/ˈprɑːmɪs/","/ˈprɑːmɪsɪz/","/ˈprɑːmɪst/","/ˈprɑːmɪsɪŋ/"]/
Meaning	I promise something is true	A commitment to do something or not do something.
Example	I swear I'm telling the truth!	I promise to help you with your homework.
Register	Informal	Neutral
How common	Top 2,000 (common)	Top 1,000 (very common)
CEFR level	-	A2
Part of speech		verb
Collocations	swear to tell the truth, swear on my life, swear under oath	faithfully, solemnly, initially, can, cannot, seem to, to, as promised, I can’t promise anything
Antonyms	-	lie, break, betray
Common mistakes	Using 'swear' without 'I' (like 'swear it's true') - it sounds unnatural., Confusing with 'promise' – 'swear' is stronger and often more emotional., Forgetting to use it only in informal settings.	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	Use in casual conversation to emphasize the truthfulness of a statement. It can express strong feelings. Not appropriate for formal contexts.	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

let me say that I swear

How I Met Your Mother › S1 E1

I didn't, I swear.

let me say that I swear

How I Met Your Mother › S1 E1

I didn't, I swear.

I swear

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: I swear vs Promise

What's the difference between I swear and Promise?

I swear: I promise something is true Promise: A commitment to do something or not do something.

Which is more formal: I swear and Promise?

Promise is the most formal of these.

Which is more common: I swear and Promise?

Promise is the most common in everyday English.

Can you show an example of each?

I swear: I swear I'm telling the truth! Promise: I promise to help you with your homework.

Can I use I swear and Promise interchangeably?

Not always. I swear 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.