Cool MateCertainly vs Definitely vs Of course vs Surely vs Undoubtedly
When to use each in English, with meaning, register, and examples.
Certainly
Definitely
Of course
Surely
Undoubtedly
| Certainly | Definitely | Of course | Surely | Undoubtedly | |
|---|---|---|---|---|---|
| Pronunciation | 🇬🇧 /["/ˈsɜːtnli/"]/🇺🇸 /["/ˈsɜːrtnli/"]/ | 🇬🇧 /["/ˈdefɪnətli/"]/🇺🇸 /["/ˈdefɪnətli/"]/ | 🇬🇧 //əv kɔːs//🇺🇸 //əv kɔrs// | 🇬🇧 /["/ˈʃʊəli//ˈʃɔːli/"]/🇺🇸 /["/ˈʃʊrli/"]/ | 🇬🇧 //ʌnˈdaʊtɪdli//🇺🇸 //ʌnˈdaʊtədli// |
| Meaning | Definitely; for sure. | For sure, without a doubt | Definitely, it's obvious. | certainly; without a doubt | Definitely; without a doubt. |
| Example | Without treatment, she will **almost certainly** die. | I definitely remember sending the letter. | Are you joining us for dinner tonight? Of course! | Surely we should do something about it? | She is undoubtedly the best candidate for the position. |
| Register | Neutral | Neutral | Neutral | Neutral | Formal |
| How common | Top 1,000 (very common) | Top 1,000 (very common) | Top 1,000 (very common) | Top 2,000 (common) | Top 5,000 (fairly common) |
| CEFR level | A2 | A2 | - | B1 | C1 |
| Part of speech | adverb | adverb | adverb | adverb | |
| Collocations | certainly agree, certainly possible, certainly not, certainly true, certainly yes | definitely agree, definitely believe, definitely know | of course not, of course yes, of course you can, of course it is | surely believe, surely know, surely must | undoubtedly true, undoubtedly clear, undoubtedly helpful |
| Antonyms | uncertainly, doubtfully | doubtfully, uncertainly | - | doubtfully, unsure | 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 it in formal writing where a different expression is needed., Confusing it with other affirmations like 'certainly' or 'definitely'. | Confusing 'surely' with 'sure' — 'sure' can be an adjective., Using 'surely' as a response when a simple 'yes' would suffice., Omitting 'surely' in a sentence where it clarifies certainty. | 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 in informal and formal situations to affirm something obvious. Avoid in highly formal writing. | Use 'surely' to express certainty. It’s appropriate in both spoken and written contexts but is more common in formal discussions. Avoid using it in very casual conversations where simpler words like 'definitely' might fit better. | Used to emphasize certainty or strong belief; typically in formal writing or speeches, not common in casual conversation. |
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Frequently asked questions: Certainly vs Definitely vs Of course vs Surely vs Undoubtedly
What's the difference between Certainly, Definitely, Of course, Surely, and Undoubtedly?
Certainly: Definitely; for sure. Definitely: For sure, without a doubt Of course: Definitely, it's obvious. Surely: certainly; without a doubt Undoubtedly: Definitely; without a doubt.
Which is more formal: Certainly, Definitely, Of course, Surely, and Undoubtedly?
Undoubtedly is the most formal of these.
Which is more advanced: Certainly, Definitely, Of course, Surely, 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. Of course: Are you joining us for dinner tonight? Of course! Surely: Surely we should do something about it? Undoubtedly: She is undoubtedly the best candidate for the position.
Can I use Certainly, Definitely, Of course, Surely, and Undoubtedly interchangeably?
Not always. Certainly, Definitely, Of course, Surely, 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.