Ten sweter jest cieplejszy niż tamten.

They are demonstratives:

• ten = this
• tamten = that

In this sentence, both refer to a masculine singular noun, sweter, so they appear in the masculine singular form.

A useful thing to notice is that tamten at the end stands by itself, but it really means tamten sweter. Polish often leaves out a repeated noun when it is obvious from context.

Because sweter is a masculine singular noun.

In Polish, words like this and that, and also adjectives, must agree with the noun in:

• gender
• number
• sometimes case

So with sweter, you get masculine singular forms:

• ten sweter
• tamten sweter
• cieplejszy sweter

If the noun were feminine, you would use ta and tamta instead.

Cieplejszy is the comparative form of ciepły.

So:

• ciepły = warm
• cieplejszy = warmer

It also agrees with sweter, which is masculine singular, so the ending is -y.

Compare:

• masculine singular: cieplejszy
• feminine singular: cieplejsza
• neuter singular: cieplejsze
• plural: cieplejsze

Polish often forms comparatives by changing the adjective stem and adding a comparative ending such as -szy or -ejszy.

Here:

• ciepły → stem ciepl-
• then the comparative becomes cieplejszy

This is the normal comparative form, and it is much more natural than trying to say bardziej ciepły in this sentence.

You do not need to memorize every rule perfectly at once, but it is good to recognize that Polish comparatives are often formed as one word, unlike English phrases such as more + adjective.

You usually should not here.

Polish can form comparisons in two main ways:

• with a simple comparative: cieplejszy
• with bardziej + adjective

But bardziej + adjective is mainly used when there is no natural simple comparative, or when the speaker wants a different style.

For ciepły, the normal and best form is cieplejszy.

So:

• natural: Ten sweter jest cieplejszy niż tamten.
• much less natural here: Ten sweter jest bardziej ciepły niż tamten.

In a normal sentence like this, jest is needed.

Polish often drops subject pronouns such as I, you, he, because the verb ending already shows the subject. But it does not normally drop the verb być in a standard sentence like this one.

So:

• correct: Ten sweter jest cieplejszy niż tamten.
• unnatural/incomplete in standard Polish: Ten sweter cieplejszy niż tamten.

You might see the verb omitted in headlines, notes, or very informal speech, but not as the normal full sentence.

Niż means than in comparisons.

It is the standard word used after a comparative adjective such as:

• większy niż = bigger than
• lepszy niż = better than
• cieplejszy niż = warmer than

So the structure is:

[something] + jest + comparative + niż + [something else]

That is exactly what is happening here.

Yes. Polish often allows both patterns:

• cieplejszy niż tamten
• cieplejszy od tamtego

But there is an important difference:

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

So both are correct:

• Ten sweter jest cieplejszy niż tamten.
• Ten sweter jest cieplejszy od tamtego.

For learners, niż is often easier at first because the compared word looks more straightforward.

The main noun phrase ten sweter is in the nominative singular, because it is the subject of the sentence.

The adjective cieplejszy agrees with that subject in masculine singular.

At the end, tamten is also understood as tamten sweter, and with niż it appears in the nominative form here.

So the basic grammar is:

• ten sweter — nominative singular masculine
• jest — 3rd person singular present of być
• cieplejszy — masculine singular comparative adjective
• niż tamten — than that one

Because the noun is understood from context.

English does this too:

• This sweater is warmer than that one.

Polish often does the same thing, except it can simply use tamten by itself, with the noun omitted.

So:

• full version: Ten sweter jest cieplejszy niż tamten sweter.
• natural version: Ten sweter jest cieplejszy niż tamten.

The shorter version is what native speakers would normally say.

A rough English-friendly approximation is:

chyep-LEHY-shy

A few helpful points:

• cie- sounds like a soft che / chye
• -lej- sounds a bit like lay
• sz sounds like English sh
• stress is on the second-to-last syllable

So the stress is:

cie-PLEJ-szy

You do not need perfect pronunciation immediately, but it helps to notice that sz is always a sh sound.

The forms would have to agree with the new noun.

For a feminine noun:

• Ta bluza jest cieplejsza niż tamta.

For a neuter noun:

• To ubranie jest cieplejsze niż tamto.

For plural:

• Te swetry są cieplejsze niż tamte.

So the pattern stays the same, but the demonstratives, the verb, and the adjective form may change to match the noun.