W tej książce jest osiemnaście stron o alfabecie.

Because w means in here, and when w expresses location, it requires the locative case.

So:

• ta książka = this book in the basic form
• w tej książce = in this book

Both words change because Polish adjectives/demonstratives and nouns have to agree in gender, number, and case.

• ta → tej
• książka → książce

So w tej książce is the correct locative form for in this book.

Tej is a form of the demonstrative ten / ta / to = this.

In this sentence, it matches książce, which is:

• feminine
• singular
• locative

So:

• basic form: ta książka = this book
• locative form: w tej książce = in this book

For an English speaker, it can help to think of tej as not a separate word to memorize on its own, but as the form this takes when it has to match a feminine singular noun in the locative.

Because książka is in the locative singular after w.

The dictionary form is:

• książka = book

But after w meaning in, you need the locative:

• w książce = in the book

When you add this, you get:

• w tej książce = in this book

So the ending -e is not random; it is part of the noun’s locative form.

This is a very common question.

In Polish, expressions with numbers like osiemnaście stron often behave like a quantity expression, especially in sentences of the type there is/there are.

So Polish says:

• jest osiemnaście stron
  literally something like there is eighteen pages

This sounds strange from an English point of view, but it is normal in Polish. The focus is on the existence of an amount, not on the pages as individual items.

So in this sentence, jest is the normal choice.

Because after 5 and higher numbers, Polish normally uses the genitive plural of the noun.

The noun is:

• strona = page

Its genitive plural is:

• stron

So:

• jedna strona = one page
• dwie / trzy / cztery strony = two / three / four pages
• pięć stron, osiemnaście stron = five pages, eighteen pages

Since osiemnaście belongs to the 5+ pattern, stron is required.

Because the preposition o meaning about requires the locative case.

The basic form is:

• alfabet = alphabet

After o:

• o alfabecie = about the alphabet

So this is the same kind of pattern as w tej książce:

• w
  • locative
• o
  • locative

This sentence has two locative phrases:

• w tej książce = in this book
• o alfabecie = about the alphabet

Yes. Strona can mean several things in Polish, including:

• page
• side
• sometimes party/side in an argument or conflict

But in this sentence, because we are talking about a book, stron clearly means pages.

So osiemnaście stron o alfabecie means eighteen pages about the alphabet.

Yes, that is grammatical, but the focus is slightly different.

• W tej książce jest osiemnaście stron o alfabecie
  focuses on what is in the book

• Ta książka ma osiemnaście stron o alfabecie
  focuses on what the book has

In many contexts, both are natural. The original sentence sounds a bit more like Within this book, there are eighteen pages about the alphabet.

Not completely. Polish word order is fairly flexible, but different orders sound more or less natural depending on emphasis.

The given order:

• W tej książce jest osiemnaście stron o alfabecie.

is neutral and natural.

If you move things around, you change the emphasis. For example, you might put w tej książce first to highlight the location, which is exactly what the sentence already does.

A learner should usually keep this order unless there is a specific reason to emphasize something else.

Because w tej książce describes location: in this book.

When w means in and shows where something is, Polish uses the locative:

• w tej książce = in this book

But w tę książkę would be into this book, with a sense of movement toward the inside, so it uses the accusative instead.

So the contrast is:

• w tej książce = location
• w tę książkę = movement into

As for w tą książkę, many native speakers say tą colloquially in some contexts, but the standard accusative feminine form is tę. In this sentence, though, neither tę nor tą is correct, because the meaning is location, so you need tej.