У мене чотири книги.

Ukrainian very often expresses possession with a structure that is literally more like at me than I have.

So:

• У мене чотири книги.
• literally: At me, four books
• natural English: I have four books

This is one of the most common ways to say have in Ukrainian.

Because мене is the form of я used after the preposition у/в in this pattern.

• я = I
• мене = me / of me depending on the structure

In у мене, the pronoun is not the subject the way I is in English. It is part of a prepositional phrase meaning roughly at me / with me.

So you say:

• у мене
• not у я

Yes, є can be added, and both versions are correct:

• У мене чотири книги.
• У мене є чотири книги.

In the present tense, Ukrainian often leaves out є when the meaning is clear. That is very normal.

A rough difference:

• У мене чотири книги. = neutral, very common
• У мене є чотири книги. = also common, sometimes a bit more explicit: I do have four books / There are four books in my possession

So the sentence without є is not incomplete.

Because after 2, 3, 4, Ukrainian nouns use a special counting form.

With книга, the pattern is:

• одна книга = one book
• дві книги = two books
• три книги = three books
• чотири книги = four books

So after чотири, книга changes to книги.

A useful contrast:

• чотири книги
• п’ять книг

After 5 and higher, the noun usually changes again.

For a learner, the simplest way to think of it is: книги is the form used after дві, три, чотири.

With книга, this form happens to look the same as other forms you may meet elsewhere, but in this sentence the important thing is the number pattern:

• 1 → книга
• 2–4 → книги
• 5+ → книг

So it is best to learn it as part of the number system rather than trying to force an English-style singular/plural idea onto it.

Yes. Я маю чотири книги is grammatical and understandable.

But У мене (є) чотири книги is often the more natural everyday way to express possession in Ukrainian.

So both mean I have four books, but:

• У мене чотири книги = very common possession pattern
• Я маю чотири книги = also correct, sometimes a bit more direct or formal depending on context

As a learner, it is very useful to get comfortable with у мене because you will hear it a lot.

Yes. у and в often alternate in Ukrainian for ease of pronunciation.

So both are possible:

• У мене чотири книги
• В мене чотири книги

The meaning does not change. The choice is mostly about sound and flow.

At the beginning of a sentence, У мене is very common, but В мене is also widely used in speech.

Yes. Ukrainian word order is more flexible than English word order.

The most neutral version is:

• У мене чотири книги.

But you could also hear things like:

• Чотири книги у мене.

That changes the emphasis a bit. For example, it may highlight four books or sound contrastive depending on context.

So the original sentence is the best neutral model to learn first.

Here is the basic pattern:

• У мене одна книга. = I have one book.
• У мене дві книги. = I have two books.
• У мене три книги. = I have three books.
• У мене чотири книги. = I have four books.
• У мене п’ять книг. = I have five books.

This is an important pattern in Ukrainian:

• 1 → singular
• 2–4 → книги
• 5+ → книг

So чотири книги fits that standard pattern exactly.

It can do both, depending on context.

In this sentence, у мене means possession:

• У мене чотири книги. = I have four books.

But in other contexts, it can be more literally at my place / with me / on me, depending on the words around it.

That is why learners often find it helpful to remember the core idea of у мене as something like with me / at me, and then let the full sentence tell them the exact English meaning.