Some abstract nouns can be used in a particular sense with a/an, but in the singular only
Some abstract nouns can be used in a particular sense with a/an, but in the singular only:
a help: My children are a great help to me. A good map would be a help.
a relief: It was a relief to sit down.
a knowledge + of: He had a good knowledge of mathematics.
a dislike/dread/hatred/horror/love + of is also possible:
a love of music a hatred of violence
a mercy/pity/shame/wonder can be used with that-clauses introduced by it:
It's a pity you weren't here. It's a shame he wasn't paid.
a fear/fears, a hope/hopes, a suspicion/suspicions
These can be used with that-clauses introduced by there:
There is a fear/There are fears that he has been murdered.