[Vocabulary] Usage of 'Bona Fides'

[Barman]

In the following sentences which one is correct?
Kindly give me the explanation.

1) His bona fides were not questioned.

2) His bona fides was not questioned.

 

[Rover_KE]

2) is correct. Bona fides means 'good faith'.

 

[teechar]

[STRIKE]In[/STRIKE] Of the following sentences which one is correct?
Kindly give me the explanation.

The first is wrong, because "bona fides" is always a plural noun (no singular equivalent).

https://dictionary.cambridge.org/dictionary/english/bona-fides

 

[Rover_KE]

Apparently I'm behind the times.

Bona fides is originally a Latin phrase meaning "good faith.'' Fides is singular in Latin and has been used as such in English. At least partially because its -es ending makes bona fides look and sound like a plural, it has developed the plural sense "credentials.'' This plural use, although criticized by some usage guides, has been increasing in recent decades in all varieties of speech and writing.

(Random House)

 

[probus]

Apparently I'm behind the times.

(Random House)

Me too. It seems a knowledge of classics has now become a disadvantage. The other day I told my brother that kudos is a singular noun meaning praise. I met with fierce resistance and on looking into it had to admit I was wrong. I might have been right 50 or 60 years ago, but English marches ever onward.

 

[teechar]

I vaguely seem to remember hearing "bona fides" (as a noun) for the first time and wondering whether it would become standard.