Apartienen a este grupo las conjunciones because, as, since. La más usada es because, as y since tienen el mismo valor semántico.

21.3.2 as, because, since = como, porque
As we didn't know the way to the theatre, we had to ask the old lady.
Como no conocimos el camino tuvimos que preguntar la señora.
He started the meeting at 8 o'clock, because he knew that it would take more than 3 hours.
Comenzó con la reunión a las ocho, porque sabía que va a durar tres horas.
The group would have to give up, since they had not enough provisions.
El grupo tendría que abandonar, porque no tenían bastante víveres.