Ten karton jest cięższy niż tamten, bo są w nim książki.

to be

Breakdown of Ten karton jest cięższy niż tamten, bo są w nim książki.

• w: in
• bo: because
• ten: this

Questions & Answers about Ten karton jest cięższy niż tamten, bo są w nim książki.

Why is it ten karton and not ta karton or to karton?

Because karton is a masculine singular noun in Polish, so the demonstrative has to match it:

• ten = masculine
• ta = feminine
• to = neuter

So:

• ten karton = this box/carton
• ta książka = this book
• to pudełko = this little box

The same agreement applies to tamten.

What do ten and tamten mean here?

They are demonstratives:

• ten = this
• tamten = that

So the contrast is:

• ten karton = this box
• tamten = that one / that box

In this sentence, Polish is comparing two boxes: this one and that one.

Why can tamten stand by itself without repeating karton?