The reason why you can't say 'give him him book' but can say 'give her her book'

As a teacher and an online tutor of English as a Second Language (ESL), one of the funniest questions I've ever got from English learners is: Why is “Give him him book” considered ungrammatical unlike “Give her her book”? If you are among these persons, don't stop reading until you get to the end. Although there might be other reasons why it is grammatically wrong to say “Give him him book”, this article discusses only the simplest reason in order to aid better understanding. 

In English grammar, there is what we call possessive pronouns. Possessive pronouns are pronouns that are used to show that something or someone belongs to you. In other words, possessive pronouns are used to show ownership. Examples of possessive pronoun are "my", "mine", "her", "hers", "his", "our", "ours", "their", "theirs", "your" and "yours".

Sentence Examples

1. This is my book.

2. This book is mine.

3. That is her pen.

4. That pen is hers.

5. This is our land.

6. This land is ours.

7. Give them their pens.

8. These pens are theirs.

9. Your house is very big.

10. The food is yours.

11. Don't hesitate to give him his pen.

12. The red bag is his.

From the aforementioned examples of possessive pronouns, you will notice that "him" does not constitute the list. This simply means that "him" is not a possessive pronoun hence can't be used to show ownership. In other words, you can't say "him book" since "him" is not a possessive pronoun. "Him" (which is the objective case of 'he') is a personal pronoun, and its gender equivalent that is used to show possession/ownership is "his". That is why we can boldly say "his book".

READ MORE ON PERSONAL PRONOUNS HERE

"His" is always used to show ownership whereas "him" is mostly used instead of a noun in the object position of a sentence.

Examples

1. The man slapped Emeka.

    The man slapped him.

2. This is Emeka's book.

    This is his book.

On the other hand, you can say "give her her book" because "her" is a personal pronoun and also a possessive pronoun. Most times, we are compelled to question the ungrammaticality of the sentence "give him him book" because of the presence of the double "her" in "give her her book" without knowing that the double "her" are very distinct, both in function and type. The first "her" in "give her her book" is personal while the second "her" is possessive. So, the sentence can be rewritten as "give Ada her book". Unlike "him", "her" has no different gender equivalent to show possession or person so it functions as a personal pronoun and a possessive pronoun.

In sum, it is very ungrammatical to say "give him him book" because "him" is not a possessive pronoun but a personal pronoun hence cannot be used to show ownership/possession.