Ten wiersz jest smutniejszy niż tamten.

Because wiersz is a masculine singular noun in Polish. Demonstratives like ten / ta / to must agree with the noun’s gender, number, and case.

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

So:

• ten wiersz = this poem
• not ta wiersz
• not to wiersz

Ten means this, and tamten means that.

So in this sentence:

• ten wiersz = this poem
• tamten = that one / that poem

Polish often uses tamten to point to something more distant, either physically or in the conversation.

Because Polish can leave out a noun when it is already understood from context.

So:

• Ten wiersz jest smutniejszy niż tamten.

really means:

• Ten wiersz jest smutniejszy niż tamten wiersz.

But repeating wiersz is unnecessary, so Polish usually omits it.

This is very similar to English this poem is sadder than that one.

In standard Polish, jest is normally needed here because it is the present-tense form of być (to be).

• Ten wiersz jest smutniejszy niż tamten. = correct standard Polish

Leaving out jest would sound nonstandard, poetic, or very elliptical in this kind of sentence.

Unlike Russian, for example, Polish usually keeps to be in the present tense in sentences like this.

Smutniejszy is the comparative form of smutny (sad).

• smutny = sad
• smutniejszy = sadder

Polish often forms comparatives by adding a suffix such as -szy or -ejszy/-iejszy, sometimes with small spelling or sound changes.

Here the stem changes a little:

• smutny → smutniejszy

You do not just add one fixed ending mechanically to every adjective, so it is best to learn comparative patterns through examples.

Yes, but smutniejszy is more natural here.

Polish has two common ways to make comparatives:

• synthetic comparative: smutniejszy = sadder
• analytic comparative: bardziej smutny = more sad

For short, common adjectives, the synthetic form is usually preferred.

So:

• Ten wiersz jest smutniejszy niż tamten. = most natural
• Ten wiersz jest bardziej smutny niż tamten. = understandable, but less natural

Niż means than in comparisons.

So:

• smutniejszy niż tamten = sadder than that one

It is the normal word to use after a comparative adjective.

Examples:

• większy niż = bigger than
• mniejszy niż = smaller than
• lepszy niż = better than

Yes. In many sentences, niż and od can both be used after a comparative, but the grammar changes slightly.

With niż:

• Ten wiersz jest smutniejszy niż tamten.

With od:

• Ten wiersz jest smutniejszy od tamtego.

Important difference:

• after niż, you get tamten
• after od, you need the genitive form: tamtego

So both are correct, but the case is different.

Because od is a preposition, and prepositions in Polish require specific cases. Od requires the genitive.

So:

• od tamtego = from/than that one

By contrast, niż is not a preposition. In a sentence like this, the second element often stays in the form you would expect from the comparison structure, so you get:

• niż tamten

That is why these two versions look different:

• smutniejszy niż tamten
• smutniejszy od tamtego

Yes. Even though it is a comparative, smutniejszy still agrees with the noun in gender, number, and usually case.

Here:

• wiersz is masculine singular
• so the adjective is smutniejszy (masculine singular)

Compare:

• Ten wiersz jest smutniejszy. = masculine
• Ta piosenka jest smutniejsza. = feminine
• To opowiadanie jest smutniejsze. = neuter
• Te wiersze są smutniejsze. = plural

No, Polish word order is fairly flexible, although some orders sound more neutral than others.

The most neutral version is:

• Ten wiersz jest smutniejszy niż tamten.

But other orders are possible for emphasis, for example:

• Smutniejszy jest ten wiersz niż tamten.
• Ten wiersz smutniejszy jest niż tamten. — more marked or literary

A learner should usually stick with the neutral order unless there is a special reason to emphasize something.

These two words can be tricky for English speakers.

• wiersz is pronounced roughly like vyersh

  • w in Polish sounds like English v
  • ie sounds like ye
  • sz sounds like English sh

• smutniejszy is roughly smoot-NYEY-shih or smoot-NYESH-shih, depending on how narrowly you describe it

  • u = oo
  • nie = something like nye
  • sz = sh
  • final y is not exactly English ee; it is a short Polish y sound

If pronunciation matters, it is best to hear native audio, because Polish consonant clusters are hard to learn from spelling alone.

Yes. All of those forms may need to change so they match the new noun.

For example:

• Ten wiersz jest smutniejszy niż tamten.
  masculine singular

• Ta piosenka jest smutniejsza niż tamta.
  feminine singular

• To opowiadanie jest smutniejsze niż tamto.
  neuter singular

• Te wiersze są smutniejsze niż tamte.
  plural

So when you swap the noun, you often have to adjust several other words too.