Sentir que: to sense, or to be sorry
Sentir has two meanings, and the mood after que tells you which one. With the indicative it means to feel, to sense: you notice that something is true. With the subjunctive it means to be sorry, the meaning of lo siento, and like other feelings about someone else's situation it takes the subjunctive.
| indicative: I sense | subjunctive: I'm sorry |
|---|---|
| Siento que estás triste. | Siento que estés triste. |
| I can tell you're sad. | I'm sorry you're sad. |
| I can tell that you are sad; talk to me. | Siento que estás triste; háblame. |
| I'm sorry that you are sad. | Siento que estés triste. |
One letter changes the whole message.
| I felt that someone was looking at me. | Sentí que alguien me miraba. |
| I'm very sorry that you weren't able to come. | Siento mucho que no hayas podido venir. |
For a past event you are sorry about now, the perfect subjunctive is the usual choice (hayas podido). When the event lies further back, the imperfect subjunctive also works: Siento que no pudieras venir el sábado.
No sabía que + indicative
When you have just found something out and accept it as a fact, no sabía que is usually followed by the indicative, with the tenses of reported speech.
| I didn't know that you spoke German. | No sabía que hablabas alemán. |
| Sorry, I didn't know that you were here. | Perdona, no sabía que estabas aquí. |
No sabía que + subjunctive
The imperfect subjunctive is also correct, and common, when the news still surprises you or you are not vouching for it: it keeps a little distance.
| I didn't know that something like that existed. | No sabía que existiera algo así. |
| I didn't know that the museum was free. | No sabía que el museo fuera gratis. |
If you are unsure, the indicative is the safe choice for a plain fact you have just learned.
