Declare vs I swear

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

Declare

Formal Top 2,000 (common) B2 verb

I swear

Informal Top 2,000 (common)

Most formal: Declare

	Declare	I swear
Pronunciation	🇬🇧 /["/dɪˈkleə(r)/","/dɪˈkleəz/","/dɪˈkleəd/","/dɪˈkleərɪŋ/"]/ 🇺🇸 /["/dɪˈkler/","/dɪˈklerz/","/dɪˈklerd/","/dɪˈklerɪŋ/"]/	🇬🇧 //aɪ swɛər// 🇺🇸 //aɪ swɛr//
Meaning	To say something officially or publicly.	I promise something is true
Example	The president will declare the new policy during the press conference.	I swear I'm telling the truth!
Register	Formal	Informal
How common	Top 2,000 (common)	Top 2,000 (common)
CEFR level	B2	-
Part of speech	verb
Collocations	virtually, immediately, promptly, to, virtually, immediately, promptly, to	swear to tell the truth, swear on my life, swear under oath
Antonyms	deny, disclaim, suppress	-
Common mistakes	Using 'declare' without an object (e.g., 'I declare' alone is often incomplete), Confusing 'declare' with 'proclaim' which has a different nuance, Saying 'declaring for' instead of 'declaring to be' when stating identity or status	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.
Usage notes	Used in formal contexts such as legal, government, or academic settings. Avoid in casual conversations. Commonly used when making announcements or stating intentions.	Use in casual conversation to emphasize the truthfulness of a statement. It can express strong feelings. Not appropriate for formal contexts.

See it in real clips

No jury can declare a man guilty unless it's sure.

Declare

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

Frequently asked questions: Declare vs I swear

What's the difference between Declare and I swear?

Declare: To say something officially or publicly. I swear: I promise something is true

Which is more formal: Declare and I swear?

Declare is the most formal of these.

Can you show an example of each?

Declare: The president will declare the new policy during the press conference. I swear: I swear I'm telling the truth!

Can I use Declare and I swear interchangeably?

Not always. Declare and I 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.