Jeho zájem je velký.

Jeho is the third-person possessive pronoun, meaning his.

In Jeho zájem je velký, it tells you whose interest it is: his interest.

A useful thing to know is that jeho is normally unchanged. Unlike many Czech words, it does not change its form to agree with the noun it goes with.

Examples:

• jeho dům = his house
• jeho kniha = his book
• jeho auto = his car

So even though dům, kniha, and auto have different genders, jeho stays jeho.

This is a very common question.

Czech uses svůj for one’s own, but only when the possessor is the subject of the same clause.

In this sentence, the subject is zájem and the possessor is he, so Czech uses jeho, not svůj.

Compare:

• Petr miluje svůj dům. = Peter loves his own house.
  
  • The subject is Petr, and the house belongs to Petr.
• Petr miluje jeho dům. = Peter loves his house.
  
  • Now the house belongs to some other male person, not Peter.

In Jeho zájem je velký, there is no reason to use svůj, because the sentence is simply describing his interest.

Zájem is in the nominative singular.

Why? Because it is the subject of the sentence. In a basic Czech sentence with to be, the subject is usually in the nominative:

• zájem = interest
• Jeho zájem je velký. = His interest is great / His interest is big.

So:

• jeho zájem = the subject
• je velký = what is being said about the subject

Je is the 3rd person singular of the verb být (to be).

So it works like English is:

• je = is

In the sentence:

• Jeho zájem je velký
• literally: His interest is big/great

Unlike Russian and some other Slavic languages, Czech normally does use the present-tense form of to be in sentences like this.

Because velký is an adjective, and it must agree with the noun zájem.

Zájem is:

• masculine
• singular
• nominative
• specifically masculine inanimate

So the adjective also takes the matching form:

• velký

Compare:

• velký zájem = great/big interest
• velká kniha = big book
• velké auto = big car

This agreement is one of the most important features of Czech grammar.

Nouns in Czech have grammatical gender: masculine, feminine, or neuter.

Zájem is a masculine noun. Its gender is grammatical, not logical. Since interest is an abstract idea, English speakers often expect no gender, but Czech nouns still belong to a gender class.

You usually learn the gender together with the noun:

• ten zájem = that interest

That tells you it is masculine.

It can suggest either, depending on context.

The basic meaning of velký is big/large, but with abstract nouns like zájem, it is often better understood as:

• great
• strong
• considerable

So Jeho zájem je velký can sound more natural in English as:

• His interest is great
• He is very interested
  depending on the context.

Czech often uses velký with abstract nouns in places where English would choose a less literal adjective.

Yes. Czech word order is more flexible than English word order.

The neutral order here is:

• Jeho zájem je velký.

But other orders are possible for emphasis or style, for example:

• Velký je jeho zájem.
• Je velký jeho zájem.
  This is less neutral and more marked.

Even when the order changes, the endings help show what belongs with what.

For a learner, the safest neutral version is:

• Jeho zájem je velký.

Czech has no articles like English a/an/the.

So zájem can mean:

• interest
• the interest
• an interest

The exact meaning depends on context.

That is why Czech learners of English often forget articles, and English speakers learning Czech often want to add them even though Czech does not use them.

Sometimes zájem can mean different things depending on context, such as:

• interest
• concern
• area of interest
• sometimes even attention

But in this sentence, with je velký, the most natural reading is simply his interest is great/strong.

So yes, zájem is a flexible word, but context decides the best English equivalent.

Yes, it is grammatical and understandable.

However, depending on context, a Czech speaker might also say something more idiomatic, such as:

• Má velký zájem. = He has great interest / He is very interested.
• Velmi ho to zajímá. = He is very interested in it.

So the given sentence is perfectly correct, but in everyday speech Czech may often prefer another structure if the context allows it.

A simple approximate pronunciation is:

• Jeho ≈ YEH-ho
• zájem ≈ ZAA-yem
• je ≈ ye
• velký ≈ VEL-kee

A more careful note:

• j in Czech sounds like English y in yes
• á is a long vowel
• ý is also a long vowel

So the sentence sounds roughly like:

• YEH-ho ZAA-yem ye VEL-kee

Yes, sometimes Czech can leave out information if the context is clear, but in this exact sentence, removing jeho changes the meaning.

• Jeho zájem je velký. = His interest is great.
• Zájem je velký. = The interest is great / Interest is great.

Without jeho, the sentence becomes more general and no longer specifically says whose interest it is.

So you should keep jeho if his is important.