What's the best way to express "could have"
I am trying to say..."It could have been a dream for all we know."
Can it be expressed as... Pudo ser un sueño por todo sabemos
From what I have researched, there are various ways to express "could have" ...
Thanks for you help.
1 Answer
Podría haber sido un sueño para todo lo que sabemos. 
http://spanish.about.com/cs/verbs/a/using_poder.htm
In the preterite or imperfect to mean "could" or "was able": Which tense you use depends on whether the reference is to a one-time event (preterite) or something occurring over a period of time (imperfect). In the preterite, poder can have the sense of "to manage to."
Examples: Pudo salir. ("He managed to leave.") No podía salir. ("He was unable to leave.") No pudo trabajar porque dormía. ("She couldn't work (that particular time) because she was sleeping.") No podía trabajar porque dormía con frecuencia. ("She couldn't work because she was often sleeping.")
