Learn Italian: Il libro è antico; esso contiene una rima perfetta. - The book is ancient; it contains a perfect rhyme.

In everyday spoken Italian, you would almost certainly omit the pronoun and just say ... ; contiene una rima perfetta. However, in formal or literary written Italian, pronouns like esso (masculine singular for objects and animals) are often used to explicitly restate the subject, providing stylistic balance or clarity after a pause like a semicolon.

Could I use lui instead of esso to mean "it" in this context?

No. While lui is the standard spoken subject pronoun for "he", it is strictly reserved for people (and sometimes pets). For inanimate masculine objects like il libro, formal written Italian uses esso. In everyday speech, you cannot substitute lui for an object; you must simply drop the pronoun altogether.

What nuance does antico give to the book compared to the more common word vecchio?

vecchio simply means "old" and can sometimes imply that an object is worn out, decrepit, or just no longer new. antico translates closer to "ancient" or "antique," elevating the book to an item of historical value, age, and prestige.

How do you conjugate contenere? Is it heavily irregular?