No lo sé o No sé

Question

I have tried searching, but can't find anything.

I have seen I don't know written as both examples above. Are they both correct and does it matter which one I use - can they be used interchangeably?

To me, no lo sé implies I don't know it as opposed to just I don't know.

I wanted to say No lo sé que decir a ti (I don't know what to say to you).

Does my sentence above make sense?

Thanks

Answer 1

I wanted to say No lo sé que decir a ti (I don't know what to say to you).

Both "lo" and "qué decirte" are the direct object, but both can't appear at the same time, so use one of these:

No sé qué decirte = No lo sé.

Also, "a ti" can only used be along with "te" to emphasize or contrast.

No hay un explicación mejor como esto. You have a great talent for explaining things clearly using very few words Lazarus :D - mistermouse, Jul 24, 2011

Answer 2

I think you would include the "lo" if you are referring to something already mentioned in the conversation.

Dónde está Juan? No lo sé

Where is Juan? I don't know.

Yeah, that makes sense. Thanks - Lachicafeliz, Jul 24, 2011

Answer 3

Thanks Lazarus, helpful and succinct as always.

If I wanted to just say I don't know then which of those do I use?

No lo sé or No sé - One of my books gives the first option and another gives the second option. Which is more commonly used in speech?

Thanks again

Just to say, "I don't know" without a specific reference, that would be "No sé." "A donde vas ahora?" "No sé." Que es parecido a "No estoy seguro." - Jeremias, Jul 24, 2011

Thanks, that's really helpful - Lachicafeliz, Jul 24, 2011