I am explaining my question with an example. From what I learnt, a book about spy is a book, probably a novel, in which one or numerous spies take major roles in the storytelling. Tom Clancy's books of the adventures of Jack Ryan are books about spy. A book on spy in one of Clancy's book could be a Ryan's training manual when the CIA had trained him. However, this source said no difference. Another said the preposition "about" connects general information with the object and "on" connects specific and detailed.

  • on a topic, about a subject. a book on spies or on a spy. about a spy and about spies, too.
    – Lambie
    Feb 2, 2022 at 18:54

1 Answer 1


A book about spy isn't idiomatic English. We would say about a spy, about spies, about spying/espionage, or books such as Tom Clancy's would be described as spy novels, spy fiction etc.

When referring to a non-fiction book, you can us both about and on, but on probably does have a stronger implication of a serious work of reference or textbook.

  • Thank you. From what you typed, A book on a subject is formal language and a book about a subject is in common use, I think. Common language is not idiomatic English. So the difference is actually not about the choice of preposition but formal or casual use of the English language.
    – Kav
    Oct 26, 2021 at 5:24
  • 1
    I didn't say that 'a book on a subject' was more formal language, I said that it usually implied a more serious, specialist kind of book. (There are reference books on English law with titles like 'Chitty on Contracts', 'Clerk and Lindsell on Torts'.) A book 'about' a topic could be a popular non-fiction work. This isn't a hard-and-fast rule - as I said, you can use both. Oct 26, 2021 at 8:25
  • Right, like a book on butterflies, for instance. You can use both the on is more sciency.
    – Lambie
    Feb 2, 2022 at 18:24

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