A gerundio instead of a clause
A gerundio at the start of a sentence can replace a whole subordinate clause. It has no conjunction, so only the context shows whether it gives a reason, a condition, a means or, with aun, a concession. It sounds compact and slightly elevated. English -ing clauses work much the same way: Knowing the truth, he said nothing.
Full clause
Aunque sabía la verdad, no dijo nada.
Although he knew the truth, he said nothing.
Gerundio
Aun sabiendo la verdad, no dijo nada.
Even knowing the truth, he said nothing.
Four meanings
Concession: aun / incluso + gerundio
Aun ganando menos, prefiero este trabajo.
Even earning less, I prefer this job.
Incluso saliendo a las seis, llegamos tarde.
Even leaving at six, we arrived late.
Cause
Siendo así las cosas, prefiero no opinar.
Things being as they are, I'd rather not comment.
Estando tan cansada, prefirió quedarse en casa.
Being so tired, she preferred to stay at home.
Condition
Saliendo ahora, llegamos a tiempo.
If we leave now, we'll be on time.
Tomando el metro, llegas en diez minutos.
If you take the underground, you'll be there in ten minutes.
Means
Ahorrando un poco cada mes, pudimos irnos a Japón.
By saving a little every month, we managed to go to Japan.
A gerundio with its own subject
If the gerundio needs a different subject from the main clause, that subject goes after the gerundio. This belongs to elevated language and occurs mostly with ser and estar. English puts it first: She being the boss, …
Siendo ella la jefa, nadie se atrevió a protestar.
Since she was the boss, nobody dared to complain.
Estando yo delante, no se atreverá a decir nada.
As long as I'm there, he won't dare say anything.
