Ten koszyk jest większy niż tamten.

Ten means this.

In Polish, demonstratives like ten / ta / to change to match the gender, number, and case of the noun they describe.

Here, koszyk is:

• masculine
• singular
• nominative

So the correct form is ten koszyk = this basket.

A few matching forms are:

• ten koszyk = this basket
• ta książka = this book
• to okno = this window

So ten is used because it agrees with koszyk.

Koszyk is in the nominative singular, which is the basic dictionary form of the noun.

It is nominative here because koszyk is the subject of the sentence:

• Ten koszyk jest większy...
• This basket is bigger...

In Polish, the subject of a sentence is usually in the nominative case.

Other forms would appear in different functions:

• koszyka = genitive/accusative, depending on context
• koszykiem = instrumental
• koszyku = locative/vocative, depending on context

But here we simply have this basket is..., so nominative koszyk is correct.

Here jest means is.

In the present tense, Polish often omits to be in some sentence types, especially when saying that one thing is another thing:

• To mój brat. = This is my brother.

But with an adjective like bigger, Polish normally uses jest:

• Ten koszyk jest większy. = This basket is bigger.

So in this sentence, jest is natural and expected.

Większy means bigger / larger. It is the comparative form.

This is an important irregular pattern. Polish does not form this comparative from duży in a simple, obvious way. Instead:

• duży = big
• większy = bigger

So you should learn większy as the comparative you use for duży.

Related forms:

• duży koszyk = a big basket
• większy koszyk = a bigger basket
• największy koszyk = the biggest basket

Because it agrees with koszyk.

Polish adjectives must match the noun they describe in:

• gender
• number
• case

Since koszyk is masculine singular nominative, the adjective also takes the masculine singular nominative form:

• większy

Compare:

• ten koszyk jest większy = this basket is bigger
• ta torba jest większa = this bag is bigger
• to pudełko jest większe = this box is bigger

So the ending changes depending on the noun.

Niż means than in comparisons.

So:

• większy niż tamten = bigger than that one

You use niż after a comparative adjective or adverb:

• starszy niż ja = older than me
• szybszy niż pociąg = faster than a train
• droższy niż ten = more expensive than this one

It is one of the standard ways to make comparisons in Polish.

Because Polish can omit the noun when it is obvious from context.

So:

• Ten koszyk jest większy niż tamten. literally means:
• This basket is bigger than that one.

The full version would be:

• Ten koszyk jest większy niż tamten koszyk.

But repeating koszyk is unnecessary, so Polish usually leaves it out, just like English often says that one instead of repeating basket.

Yes, tamten means that, often with the sense of that one over there or that other one.

In contrast:

• ten = this
• tamten = that

So the sentence sets up a contrast:

• ten koszyk = this basket
• tamten = that one / that basket

Like ten, tamten changes form to agree with gender, number, and case:

• tamten koszyk = that basket
• tamta torba = that bag
• tamto pudełko = that box

Yes. Agreement is very important in Polish.

Here koszyk is masculine singular, so the other words connected to it also appear in masculine singular forms:

• ten → masculine singular
• większy → masculine singular
• tamten → masculine singular

That is why the sentence looks the way it does.

If the noun were feminine, the forms would change:

• Ta torba jest większa niż tamta.
• This bag is bigger than that one.

If it were neuter:

• To pudełko jest większe niż tamto.
• This box is bigger than that one.

Yes. That is also correct.

Polish commonly expresses than in two main ways here:

1. niż

   • Ten koszyk jest większy niż tamten.

2. od

   • genitive
   • Ten koszyk jest większy od tamtego.
   • literally: This basket is bigger from that one, but naturally it means than that one

Notice the difference:

• after niż, you often get a form matching the omitted noun: tamten
• after od, you need the genitive: tamtego

Both versions are natural.

Here tamten is effectively nominative masculine singular, because it stands for tamten koszyk.

So:

• Ten koszyk jest większy niż tamten [koszyk].

Since the omitted noun would be nominative, tamten stays in that matching form.

But if you use od, the case changes:

• większy od tamtego [koszyka]

So this is a useful contrast:

• niż tamten
• od tamtego

The basic order here is very natural:

• Ten koszyk jest większy niż tamten.

Polish word order is more flexible than English, but not every change sounds equally neutral.

This sentence is the most straightforward version for everyday use.

You may hear variations for emphasis, but they are more marked:

• Większy jest ten koszyk niż tamten.
• Ten koszyk większy jest niż tamten.

These are possible in special contexts, but the standard learner-friendly version is:

• Ten koszyk jest większy niż tamten.

Niż is pronounced roughly like neezh, with a soft n sound and a zh sound at the end.

Important points:

• ń/ni before a vowel-like sound gives a soft n
• ż sounds like the s in measure

So niż is approximately:

• neezh

For learners, the biggest thing is to avoid pronouncing it like English nidge or nish.

And yes, niż and niź are different spellings, but niż is the normal word meaning than in this sentence.

A rough English-friendly approximation is:

• VYENG-kshih

But that is only approximate.

A few useful pronunciation notes:

• w in Polish sounds like English v
• ę is a nasal vowel; before certain consonants it may sound somewhat like en/em
• ksz in większy creates a cluster similar to ksh
• sz sounds like English sh
• final y is not exactly English ee; it is a short central vowel

So większy can be challenging, and that is normal. It is best learned by listening and repeating.

Koszyk is a normal and common word for basket, especially a small basket.

It is a diminutive-looking form historically, but in modern Polish it is very often just the ordinary everyday word.

Depending on context, Polish may also use other words, but koszyk is completely natural here:

• shopping basket
• picnic basket
• small basket

So for this sentence, koszyk is a very normal choice.