Cool MateCertainly vs Definitely vs Sure as he's born vs Undoubtedly
When to use each in English, with meaning, register, and examples.
Certainly
Definitely
Sure as he's born
Undoubtedly
| Certainly | Definitely | Sure as he's born | Undoubtedly | |
|---|---|---|---|---|
| Pronunciation | 🇬🇧 /["/ˈsɜːtnli/"]/🇺🇸 /["/ˈsɜːrtnli/"]/ | 🇬🇧 /["/ˈdefɪnətli/"]/🇺🇸 /["/ˈdefɪnətli/"]/ | 🇬🇧 //ʃʊə əz hiːz bɔːn//🇺🇸 //ʃʊr əz hiz bɔrn// | 🇬🇧 //ʌnˈdaʊtɪdli//🇺🇸 //ʌnˈdaʊtədli// |
| Meaning | Definitely; for sure. | For sure, without a doubt | certain or sure | Definitely; without a doubt. |
| Example | Without treatment, she will **almost certainly** die. | I definitely remember sending the letter. | I will be there tomorrow, sure as he's born. | She is undoubtedly the best candidate for the position. |
| Register | Neutral | Neutral | Informal | Formal |
| How common | Top 1,000 (very common) | Top 1,000 (very common) | Beyond 10,000 (less common) | Top 5,000 (fairly common) |
| CEFR level | A2 | A2 | - | C1 |
| Part of speech | adverb | adverb | adverb | |
| Collocations | certainly agree, certainly possible, certainly not, certainly true, certainly yes | definitely agree, definitely believe, definitely know | sure as can be, sure as usual | undoubtedly true, undoubtedly clear, undoubtedly helpful |
| Antonyms | uncertainly, doubtfully | doubtfully, uncertainly | uncertain, unlikely, doubtful | doubtfully, questionably, uncertainly |
| Common mistakes | 'Certainly' is often incorrectly used in place of 'certain' in adjectives., Learners might confuse 'certainly' with 'definitely' without noticing the subtle nuance., Some learners use 'certainly' in inappropriate contexts, such as casual greetings. | Often confused with 'defiantly' which means resisting authority., Sometimes spelled incorrectly as 'definately'. | Using in formal writing contexts, Confusing with similar expressions like 'sure as sugar', Misplacing the phrase within sentences | Confused with 'undoubtably', which is incorrect., Omitting it when certainty is implied., Using it in informal contexts where 'definitely' is more suitable. |
| Usage notes | Use 'certainly' when you want to emphasize affirmation or agreement. It is more formal than 'sure' and works well in professional settings, but might feel too strong in casual conversations. | Use 'definitely' to emphasize certainty. It fits well in both spoken and written English. Avoid using it in overly formal contexts where alternatives like 'certainly' might be more suitable. | Used often in spoken language, this phrase conveys strong certainty about something. It's not typically used in formal writing or situations. | Used to emphasize certainty or strong belief; typically in formal writing or speeches, not common in casual conversation. |
See it in real clips
Frequently asked questions: Certainly vs Definitely vs Sure as he's born vs Undoubtedly
What's the difference between Certainly, Definitely, Sure as he's born, and Undoubtedly?
Certainly: Definitely; for sure. Definitely: For sure, without a doubt Sure as he's born: certain or sure Undoubtedly: Definitely; without a doubt.
Which is more formal: Certainly, Definitely, Sure as he's born, and Undoubtedly?
Undoubtedly is the most formal of these.
Which is more advanced: Certainly, Definitely, Sure as he's born, and Undoubtedly?
Undoubtedly is the highest level, at C1, on the CEFR scale.
Can you show an example of each?
Certainly: Without treatment, she will **almost certainly** die. Definitely: I definitely remember sending the letter. Sure as he's born: I will be there tomorrow, sure as he's born. Undoubtedly: She is undoubtedly the best candidate for the position.
Can I use Certainly, Definitely, Sure as he's born, and Undoubtedly interchangeably?
Not always. Certainly, Definitely, Sure as he's born, and Undoubtedly 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.