Key Facts
- Hangul: 성실하다 (seongsilhada)
- Meaning: sincere/diligent
- Level: B1
- Part of speech: adjective
- Stem: 성실하
- Conjugation class: 하다 type
- Grammar: Describes a person's attitude; the adverb 성실하게 pairs with verbs like 일하다.
- Usage: A key praise word in job and school contexts.
What Does 성실하다 Mean?
성실하다 describes someone who works faithfully and reliably, as in 성실한 사람 or 성실하게 일하다. It mixes diligence with honesty, which is why employers praise it.
It is slightly formal and fits phrases like 성실한 태도 and 성실하게 공부하다.
How Do You Pronounce 성실하다?
The dictionary form has no sound change; 성 and 실 are read as spelled. The formal present 성실합니다 is [성실함니다] and the formal past 성실했습니다 is [성실핻씀니다].
How Do You Use 성실하다 in a Sentence?
우리 직원은 아주 성실해요.
Our employee is very diligent.
우리 직원은 is the topic, with 아주 as intensifier.
성실한 학생이 일등을 했어요.
The diligent student came first.
성실한 modifies 학생이, and 일등을 했어요 is the result.
그는 성실해서 인기가 많아요.
He is diligent, so he is popular.
성실해서 gives the reason for 인기가 많아요.
How Does Seongsilhada Conjugation Work?
성실하다 is a 하다 adjective: 성실해요, 성실했어요, 성실해서. The modifier is 성실한, the honorific is 성실하세요, and the negative is 성실하지 않아요.
성실하다
| Form | Korean | Romanization | Rule |
|---|---|---|---|
| Polite present | 성실해요 | ||
| Polite past | 성실했어요 | ||
| Polite future (plan) | 성실할 거예요 | ||
| Polite future (intention or guess) | 성실하겠어요 | ||
| Formal present | 성실합니다 | ||
| Formal past | 성실했습니다 | ||
| Formal future | 성실할 것입니다 | ||
| Casual present | 성실해 | ||
| Casual past | 성실했어 | ||
| Casual future | 성실할 거야 | ||
| Honorific polite | 성실하세요 | ||
| Because / and then | 성실해서 | ||
| If (conditional) | 성실하면 | ||
| Present modifier (before a noun) | 성실한 | ||
| Past modifier (before a noun) | 성실했던 | ||
| Future modifier (before a noun) | 성실할 | ||
| Negative with 안 (short) | 안 성실해요 | ||
| Negative (long form) | 성실하지 않아요 |
No want-to row: -고 싶다 suits verbs.
Sound Changes
| Form | Korean | Sounds like |
|---|---|---|
| Polite past | 성실했어요 | [성실해써요] |
| Polite future | 성실할 거예요 | [성실할꺼예요] |
| Polite future guess | 성실하겠어요 | [성실하게써요] |
| Formal present | 성실합니다 | [성실함니다] |
| Formal past | 성실했습니다 | [성실핻씀니다] |
| Formal future | 성실할 것입니다 | [성실할꺼심니다] |
| Casual past | 성실했어 | [성실해써] |
| Casual future | 성실할 거야 | [성실할꺼야] |
| Past modifier | 성실했던 | [성실핻떤] |
| Long negative | 성실하지 않아요 | [성실하지 아나요] |
성실하다 Forms to Reach for First
- Politely (sincere/diligent): 성실해요
- Earlier, in the past (sincere/diligent): 성실했어요
- Giving the reason (sincere/diligent): 성실해서
- If the condition holds (sincere/diligent): 성실하면
- Before a noun (sincere/diligent): 성실한, or 성실했던 for the past
- Denying it (sincere/diligent): 성실하지 않아요
- Honorific, about a respected person (sincere/diligent): 성실하세요
Common Mistake
Wrong: ✗ 성실이 해요
Correct: ✓ 성실해요
Why: 성실 alone is a noun meaning sincerity, so adding 이 해요 is wrong. The adjective is 성실하다 and the polite form is 성실해요.
When Does 성실하다 Fit Best?
Use 성실하다 for dependability. When you only mean busy and active, 부지런하다 is closer. Typical partners are 태도, 사람 and 학생, and the adverb 성실하게 goes before verbs such as 일하다 and 공부하다. In a job context the word is a compliment about reliability, so teachers and managers use it.
What Is Easy to Confuse with 성실하다?
| Word | How to tell it from 성실하다 |
|---|---|
| 부지런하다 | 부지런하다 is being active and not idle; 성실하다 adds being honest and dependable in your duties. |
| 솔직하다 | 솔직하다 is frankness in speech; 성실하다 is faithfulness in work and attitude. |
Recommending a Project Partner
Two classmates are choosing someone for a group assignment. One remembers working with Minho last term and recommends him for his dependable attitude.
Jisu
민호 씨는 성실해요?
Minho ssineun seongsilhaeyo?
Is Minho diligent and reliable?
Alex
네. 지난 학기에도 성실했어요.
Ne. Jinan hakgiedo seongsilhaesseoyo.
Yes. He was diligent last term too.
Jisu
성실한 사람이면 같이 일하고 싶어요.
Seongsilhan saramimyeon gachi ilhago sipeoyo.
If he’s dependable, I’d like to work with him.
성실해요 asks about a trait, 성실했어요 supplies evidence from an earlier period, and 성실한 puts the trait before 사람. 일하고 싶어요 expresses a wish to work; the wish ending belongs to 일하다, rather than to the adjective 성실하다.
Collocations for Study and Work
성실한 태도 means a conscientious attitude. It praises how someone approaches a responsibility: taking it seriously and following through. The phrase is useful when the speaker wants to evaluate effort and care without claiming that the person is the most talented or experienced.
성실하게 일하다 and 성실하게 공부하다 mean to work and study diligently. The adverb 성실하게 focuses on the manner of doing the activity. You may use it when discussing steady preparation, completing assignments or carrying out ordinary duties carefully. It does not give a number of hours worked.
성실히 is another adverb meaning faithfully or conscientiously. You may encounter 성실히 답변하다, “to answer conscientiously”, in more formal writing. Here the quality applies to giving a careful, responsible response. It is broader than saying that the answer is emotionally heartfelt.
Where Will You Read 성실하다?
School comments, recommendations and job advertisements are natural settings. 성실한 학생 praises a student’s attitude to study, while 성실한 직원 praises an employee’s dependable approach. A teacher can value this quality even when a learner still needs help understanding the material.
In a job advertisement, 성실한 can describe the kind of person an employer wants. Read the noun and surrounding duties to understand the expectation. The adjective itself does not specify a qualification, a skill level or a particular work schedule. It describes character and conduct in carrying out the role.
When introducing yourself, 성실합니다 is grammatically natural, but a concrete example makes the claim clearer. Finishing a group task on time or preparing consistently gives the listener something to connect to the word. 성실하다 evaluates a pattern of responsible conduct, so context helps distinguish it from a general compliment.
A result and an attitude are separate pieces of information. The example about the student coming first states both: 성실한 describes the student, and 일등을 했어요 reports the result. The adjective alone would not tell you the student’s score or position in the class.
Sincerity, Honesty and Activity Are Different
English “sincere” can describe a heartfelt apology or feeling. 성실하다 most naturally concerns a faithful, conscientious attitude toward what someone does. For frank speech, 솔직하다 is often the relevant comparison. The existing contrast table helps separate honest expression from dependable conduct.
부지런하다 emphasizes being active and industrious. 성실하다 emphasizes taking responsibilities seriously. A person may show both qualities, but a busy day alone does not establish dependability. Conversely, someone who works calmly and carefully can still be 성실하다 without seeming constantly active.
성실 is the noun “sincerity” or “conscientiousness”, and 성실하다 is the adjective. Keep the full adjective together in 성실해요. 성실한 belongs before a noun; 성실하게 belongs before an action. The different endings are useful clues when you read a recommendation that contains several descriptions of someone’s work.
성실하지 않아요 denies the quality and can sound like a substantial criticism of someone’s reliability. If you only mean that a person made one mistake, describe the mistake. The adjective normally invites a judgment about their broader attitude rather than just one outcome.
| Related word | Meaning | Note |
|---|---|---|
| 태도 | attitude | 성실한 태도 evaluates the approach to a responsibility. |
| 책임감 | sense of responsibility | Useful when explaining why someone is dependable. |
| 노력 | effort | Names the effort someone puts into a task. |
| 부지런하다 | industrious / diligent | Highlights activity and willingness to work. |
For other character descriptions, use the personality vocabulary lesson.
Mini Drill: Conscientious Work
- Complete “a diligent student”: ____ 학생.
- Give the polite present of 성실하다.
- Give the polite past for last term’s conduct.
- Give the long negative.
Show drill answers
- 성실한 학생.
- 성실해요.
- 성실했어요.
- 성실하지 않아요.
Quick Self-Test
- Does 성실한 학생 necessarily mean the top-scoring student?
- Which is closer to frankness in speech: 성실하다 or 솔직하다?
- In 성실하게 일하다, what does 성실하게 describe?
Show answers
- No. It praises a conscientious attitude, rather than a rank.
- 솔직하다.
- The manner of working: faithfully and diligently.
Frequently Asked Questions
What Is the Polite Present of 성실하다?
성실해요.
How Is It Different from 부지런하다?
부지런하다 is being active and not idle; 성실하다 adds being honest and dependable.
How Do I Say 'Work Diligently'?
성실하게 일하다.
What Is the Opposite?
게으르다 is the usual contrast, meaning lazy.
Which Words Are Related to 성실하다?
What Should You Learn Next?
Compare 성실하다 with 부지런하다 and 솔직하다, then see how 게으르다 acts as the opposite. The pattern is explained in how 하다 words become 해요. Then run another word through the Korean verb conjugator or browse the Korean verb dictionary.