I looked in the dictionary and noticed that in has the meaning of "concerning something."


But I am not quite sure if I can use in to mean "concerning something" in any condition.

For example:

A book concerning theology.

Could I express it this way:

A book in theology.

  • "Concerning something" is a poorly worded definition. Better might have been with respect to. "Three meters in length" and "She is not lacking in courage". We would say "A book on theology" or "A book about theology" or even "A book concerning theology".
    – TimR
    Commented May 24, 2016 at 10:24

2 Answers 2


No, you cannot use in to describe the subject of a book.

This definition of in explains it better, describing this meaning as a characteristic. Looking at the three examples quoted in your link, courage and length can reasonably be described as characteristics: I guess you could says that richness in minerals is a characteristic.

She was not lacking in courage.

a country rich in minerals

three metres in length

here are the examples from the cambridge dictionary:

The new version is worse in every respect

Are the two bags equal in weight?

She's deaf in her left ear.

For the last one, deafness in the left ear migh be a considered a characteristic.


As far as a branch of knowledge is concerned, the preposition is "on": A book on theology, or just a theology book.

  • If you are talking about a book, it is a book on theology, but you would get a degree in theology.
    – JavaLatte
    Commented May 24, 2016 at 15:29

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