Using 'Ser' instead of 'Estar'
Mistake: “Saying 'No soy seguro/a.'”
Correction: Always say 'No estoy seguro/a.'
How to say
I am not sure
in SpanishNo estoy seguro/a
no ehs-TOY seh-GOO-roh/ah
This is the most direct and universally understood way to say 'I am not sure.' Remember to change the ending: use 'seguro' if you're male and 'segura' if you're female.
When you're faced with a choice and don't know the right answer, 'No estoy seguro/a' is the perfect phrase.
🎬Watch & Learn
I am not sure — in Spanish
💬Other Ways to Say It
No sé
★★★★★
no SEH
neutral🌍
Literally 'I don't know.' This is extremely common and often used interchangeably with 'No estoy seguro/a', though it technically implies a lack of information rather than a lack of confidence.
When to use: Perfect for quick, everyday responses when you don't have the answer to a factual question. '¿A qué hora cierra la tienda?' 'No sé.'
No lo tengo claro
★★★★☆
no lo TEN-go KLAH-roh
neutral🌍
This translates to 'I don't have it clear' or 'It's not clear to me.' It suggests you've received information but are still confused or haven't fully processed it.
When to use: Use this when you're trying to understand a plan, an explanation, or instructions but something is still fuzzy. 'No lo tengo claro si debemos girar aquí o en la próxima calle.'
No sabría decirte
★★★★☆
no sah-BREE-ah deh-SEER-teh
informal🌍
A softer, more polite way to say 'I don't know.' It literally means 'I wouldn't know how to tell you.' It sounds a little less blunt than a simple 'No sé.'
When to use: When a stranger asks you for directions you don't know, or when you want to be particularly gentle in admitting you don't have the information someone needs.
Tengo mis dudas
★★★☆☆
TEN-go mees DOO-dahs
neutral🌍
This means 'I have my doubts.' It's used when you are skeptical or uncertain about the validity or outcome of something. It implies you've thought about it and are leaning towards 'no.'
When to use: When someone presents a plan that sounds a bit too good to be true. 'Él dice que puede arreglarlo en una hora, pero tengo mis dudas.'
No estoy del todo seguro/a
★★★☆☆
no ehs-TOY del TOH-doh seh-GOO-roh/ah
neutral🌍
Meaning 'I'm not entirely sure' or 'I'm not completely sure.' This phrase softens your uncertainty, suggesting you have some idea but aren't 100% confident.
When to use: When you think you know the answer but don't want to commit fully. 'Creo que la reunión es a las 3, pero no estoy del todo seguro.'
Quién sabe
★★★★☆
kyen SAH-beh
informal🌍
A very common, slightly colloquial phrase that means 'Who knows?' It's often used with a shrug and can sometimes imply that nobody really knows the answer.
When to use: In casual conversations with friends about uncertain future events. '¿Crees que lloverá mañana?' '¡Quién sabe!'
A saber
★★☆☆☆
ah sah-BEAR
informal🇪🇸
This is very common in Spain and functions exactly like 'Quién sabe.' It's a quick, informal way to express that the answer is unknown.
When to use: Primarily in Spain in casual settings. '¿Dónde se metió Juan?' 'A saber.'
🔑Key Words
Key Words to learn:
📊Quick Comparison
Here's a quick guide to help you choose the best way to express uncertainty in different situations.
| Phrase | Formality | Best For | Avoid When |
|---|---|---|---|
| No estoy seguro/a | Neutral | Expressing personal uncertainty or lack of confidence about a decision or opinion. | It's perfectly fine in almost any situation, so no need to avoid it. |
| No sé | Neutral | Quickly stating you lack a piece of factual information. It's direct and very common. | It can sound a bit blunt or unhelpful if you don't soften it. |
| No sabría decirte | Informal / Polite | Being polite when you can't help someone, especially a stranger. | In very formal writing; it's more of a conversational phrase. |
| Tengo mis dudas | Neutral | Showing skepticism or suggesting you think something might not work or be true. | You want to sound completely neutral; this phrase implies a bit of negative judgment. |
📈Difficulty Level
Overall Difficulty:beginnerMaster in a few hours
Pronunciation2/5
The sounds are very straightforward for English speakers. The main challenge is remembering to pronounce the final 'o' or 'a' clearly.
Grammar3/5
The main grammatical hurdles are remembering to use 'estar' instead of 'ser' and matching the gender of 'seguro/a' to the speaker. These are common challenges for beginners.
Cultural Nuance2/5
The phrase is quite direct, but knowing when to use softer variations like 'No sabría decirte' adds a layer of politeness that is culturally important.
Key Challenges:
- The 'Ser vs. Estar' distinction
- Remembering gender agreement ('seguro' vs. 'segura')
💡Examples in Action
Trying to find a location while traveling.A2
No estoy segura de si esta es la dirección correcta.
I'm not sure if this is the right address.
Casual conversation between friends.A2
¿Vas a venir a la fiesta el sábado? — La verdad, no sé todavía, depende del trabajo.
Are you coming to the party on Saturday? — Honestly, I don't know yet, it depends on work.
A professional or business setting.B1
El plan suena interesante, pero tengo mis dudas sobre el presupuesto.
The plan sounds interesting, but I have my doubts about the budget.
Politely asking a stranger for directions.B1
Disculpe, ¿sabe dónde está el banco? — Uf, no sabría decirle, no soy de por aquí.
Excuse me, do you know where the bank is? — Oh, I couldn't tell you, I'm not from around here.
🌍Cultural Context
Politeness and Hedging
In many Spanish-speaking cultures, directly saying 'no' or disagreeing can be seen as impolite. Using phrases like 'No estoy seguro/a' or 'No lo tengo claro' is a common, softer way to express disagreement or hesitation without causing offense.
'No Sé' vs. 'No Estoy Seguro'
While often used interchangeably, there's a subtle difference. 'No sé' (I don't know) implies a lack of facts or information. 'No estoy seguro/a' (I'm not sure) implies a lack of confidence or certainty, even if you have some information. Choosing the right one can make you sound more precise.
The Conversational Shrug
Expressions like 'Quién sabe' (Who knows?) or the Argentine 'Qué sé yo' (What do I know?) are often accompanied by a shrug. They're conversational fillers that convey a sense of shared uncertainty, making the conversation feel more relaxed and collaborative.
❌ Common Pitfalls
Forgetting Gender Agreement
Mistake: “A female speaker saying 'No estoy seguro.'”
Correction: A female speaker must say 'No estoy segura.'
Confusing 'No Sé' and 'No Puedo'
Mistake: “Using 'No sé' when you mean you are unable to do something.”
Correction: Use 'No puedo' (I can't) for ability, 'No sé' for knowledge.
💡Pro Tips
Match the Ending to Your Gender
This is a must! Always remember to use 'seguro' if you're a man and 'segura' if you're a woman. It's a small detail that makes a big difference in sounding natural.
Soften Your Uncertainty
To sound more natural and less abrupt, add a little filler word at the beginning. Phrases like 'Pues, no estoy seguro...' (Well, I'm not sure...) or 'La verdad, no sé...' (To be honest, I don't know...) are very common in conversation.
Choose Your Phrase Based on Context
Use 'No sé' for quick, factual questions. Use 'No estoy seguro/a' when you're weighing options or expressing personal confidence. Use 'No sabría decirte' to be extra polite with strangers.
🗺️Regional Variations
🇪🇸
Spain
Preferred:No estoy seguro/a, No lo tengo claro
Pronunciation:The 's' sound is often softer, almost like a 'th' in some southern regions (ceceo/seseo). The 'd' in 'duda' is also very soft.
Alternatives:
A saberNi idea
The phrase 'A saber' is extremely common in Spain as a stand-in for 'Who knows?' and is a hallmark of casual Castilian Spanish. 'No lo tengo claro' is also used very frequently.
🇲🇽
Mexico
Preferred:No estoy seguro/a, No sé
Pronunciation:Pronunciation is generally very clear and closely matches the standard pronunciation guide. Vowels are pure and consonants are distinct.
Alternatives:
Quién sabePues, no sabría decirte
Mexicans often use fillers like 'pues' or 'híjole' before expressing uncertainty to soften the phrase. For example, 'Híjole, pues no estoy seguro.' This adds a very natural, conversational flavor.
🇦🇷
Argentina
Preferred:No estoy seguro/a, No sé
Pronunciation:The 'y' and 'll' sounds are pronounced with a distinct 'sh' or 'zh' sound (sheísmo/zheísmo). The intonation has a characteristic melodic, almost Italian-like rhythm.
Alternatives:
Qué sé yoNi idea
The phrase 'Qué sé yo' (literally 'What do I know?') is an extremely common and iconic Argentine way to express 'I don't know' or 'Who knows?'. It's used constantly in casual conversation.
💬What Comes Next?
After you say you're not sure about a plan
They say:
¿Por qué? ¿Qué no te convence?
Why? What doesn't convince you?
→
You respond:
Necesito pensarlo un poco más.
I need to think about it a little more.
You tell a friend you don't know the answer to their question
They say:
Bueno, no te preocupes.
Well, don't worry about it.
→
You respond:
Pregúntale a María, quizás ella sepa.
Ask María, maybe she knows.
You express doubt about a project at work
They say:
Entiendo. ¿Qué propones entonces?
I understand. What do you propose then?
→
You respond:
Quizás podríamos analizar otras opciones.
Maybe we could analyze other options.
🧠Memory Tricks
Think: 'To be sure is a STATE of mind, so you must use ESTAR.' This helps you remember to say 'estoy seguro' and not the incorrect 'soy seguro'.
This links the grammatical rule (using 'estar' for states/conditions) to a simple, memorable concept, preventing the common 'ser' vs. 'estar' mistake.
Imagine a security guard named 'Seguro'. If you're not sure, you're 'No estoy Seguro' (not with the security guard).
This silly visual association connects the sound of the Spanish word 'seguro' with the English concept of being secure or sure.
🔄How It Differs from English
The biggest difference is grammatical. English uses one verb 'to be' ('I am'), while Spanish requires a choice between 'ser' and 'estar'. Since being unsure is a temporary state, you must use 'estar'. Additionally, English adjectives don't change, but in Spanish, 'seguro' must change to 'segura' to match the speaker's gender, a concept that doesn't exist for this type of phrase in English.
The direct translation 'No estoy seguro' is neutral in directness, similar to English. However, Spanish speakers often prefer more indirect or polite variations like 'No sabría decirte' in situations where an English speaker might just say 'I don't know,' making Spanish conversational culture slightly less direct in these cases.
False Friends & Common Confusions:
"I am not secure."
Why it''s different: While 'seguro' can mean 'secure' or 'safe', in the context of 'No estoy seguro', it means 'sure' as in 'certain'. Saying 'I am not secure' in English usually implies a lack of safety or stability, which is a different meaning.
Use instead: 'No estoy seguro/a' translates to 'I am not sure.' To say 'I don't feel safe,' you would say 'No me siento seguro/a.'
🎯Your Learning Path
➡️ Learn Next:
How to say 'I think so'
It's the natural next step after uncertainty, allowing you to express a tentative positive opinion.
How to say 'maybe'
Words like 'quizás' and 'tal vez' are essential tools for expressing different levels of certainty.
How to say 'I don't understand'
If you're not sure because you lack clarity, this phrase ('No entiendo') is what you need to ask for help.
How to ask for an opinion
After stating your own uncertainty, you'll often want to ask someone else what they think, using phrases like '¿Qué piensas tú?'
✏️Test Your Knowledge
Quick Quiz: I am not sure
Question 1 of 3
A woman wants to say she's not sure if the store is open. What should she say?
Use phrases naturally, not mechanically
Knowing a phrase is one thing — using it at the right moment is another. Read 200+ illustrated and narrated Spanish stories to see phrases in the contexts where they actually belong.
Frequently Asked Questions
What is the real difference between 'No sé' and 'No estoy seguro'?
Think of it like this: 'No sé' is about a lack of knowledge (your brain is empty on the topic). 'No estoy seguro/a' is about a lack of confidence (you might have some info, but you're not certain it's correct). In many casual cases they are interchangeable, but this subtle difference can make you sound more precise.
Why do I have to change the ending to 'segura' if I'm a woman?
In Spanish, adjectives (describing words) almost always have to match the gender and number of the noun they're describing. When you say 'Yo no estoy...', the adjective 'seguro/a' is describing 'Yo' (you). So, it must match your gender.
Is it ever correct to say 'No soy seguro'?
No, it's a very common mistake for English speakers. 'Ser' (soy) is for permanent characteristics or identity, while 'estar' (estoy) is for temporary states, conditions, and locations. Being 'sure' is considered a temporary state of mind, so you must always use 'estar'.
How can I say 'I'm not sure' in a more formal or professional setting?
'No estoy seguro/a' is perfectly acceptable in formal settings. For extra formality, you could say 'No tengo la certeza' (I don't have the certainty) or 'Necesitaría confirmar esa información' (I would need to confirm that information).
What's a very casual or slang way to say 'I'm not sure' with friends?
With friends, '¡Quién sabe!' is very common. You could also use 'Ni idea' which is like saying 'No idea' or 'Beats me!' In Argentina, 'Qué sé yo' is extremely common. These are great for informal chats.
Can I use 'No estoy seguro' to express doubt about someone else?
Yes, absolutely. You can say 'No estoy seguro de que él pueda hacerlo' (I'm not sure that he can do it). This is a great way to express your reservations about a situation or another person's abilities.
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