Denoting Past possibility : "Could be" or "could have been"

Dear Friends,

I had known that past possibility can be denoted by either "migh have been" or "could have been" until I read in A Student's Grammar of the English Language (By Sidney Greenbaum and Randolph Quirk) that "Could be" can also be used to denote the same.

For example:

In those days, transatlantic voyage could be dengerous
(=possibility)

I think it should have been:
In those days, transatlantic voyage could/might have been dengerous.

I am not sure how one can denote past possiblity with  using "could be"  instead of "could have been"

The same account has been found in the writers' "A comprehensive grammar of the English Language"

As two formidable names are associated with these accounts, this doubt is really nagging me.

Could anyone please help me in this regard.

Best Regards,
Sabya

In those days, transatlantic voyage could be dangerous.

Yes.  There really was the potential for danger when making such trips in those days.  This is the correct way to say it.

I think it should have been: ...could/might have been....

No.  Don't change it.  If you say that transatlantic voyage could have been dangerous (or might have been dangerous), you're saying that you're not sure.  You're saying that maybe there was danger and maybe there wasn't.  This is still possibility, but a different kind of possibility than indicated in the first example.

In the first example there is a true likelihood of danger.  There could be danger at that time.  In that sense, "Danger was certainly possible then."  (This usage almost requires an adverbial expression indicating past time.)
In the second example you don't know if there was danger or not.  There could have been danger at that time.  In that sense, "Maybe danger was possible then."

Compare:

During the Middle Ages people could be accused of the "crime" of witchcraft.  (It certainly was a possibility.  It often happened.)
Historians don't know what happened to the medieval philosopher Jankovitius.  For all they know, he could have been accused of witchcraft and sent to prison.  (Maybe he was accused and imprisoned; maybe not.  It was possible, but nobody knows.)

CJ

Ah, yes.  So true.  My brain just automatically changed it to transatlantic travel since it was concentrating on other matters at the time!

CJ

Very insightful thread. Thank You.

Grammar Geek,

You are right, voyage is a countable noun so requires a determiner. Also, I am sorry for the typo "dengerous".

Best Regards,
Sabya