Taj dečak je moj brat.

• Taj = that
• dečak = boy
• je = is
• moj = my
• brat = brother

So the sentence literally matches English word-for-word very closely: That boy is my brother.

Because taj has to agree with dečak in gender, number, and case.

Here, dečak is:

• masculine
• singular
• nominative

So the correct form is taj.

Compare:

• taj dečak = that boy masculine
• ta devojka = that girl feminine
• to dete = that child neuter

In Serbian, nouns have grammatical gender. Dečak means boy, so it is naturally masculine, and grammatically it is masculine too.

Because dečak is masculine, words that go with it must match:

• taj dečak
• not ta dečak
• not to dečak

Je is the 3rd person singular present tense of the verb biti, which means to be.

So:

• ja sam = I am
• ti si = you are
• on/ona/ono je = he/she/it is

In this sentence, je means is.

Because Serbian usually does not need a subject pronoun if the meaning is already clear.

English often requires a subject:

• He is...
• It is...

But Serbian often leaves it out:

• Je moj brat would still contain is, though this exact wording would sound incomplete without context.

In Taj dečak je moj brat, the subject is already stated as Taj dečak, so no extra pronoun is needed.

Because moj must agree with brat.

Brat is:

• masculine
• singular
• nominative

So the correct possessive form is moj.

Compare:

• moj brat = my brother
• moja sestra = my sister
• moje dete = my child
• moji prijatelji = my friends

Because in this kind of sentence, both nouns are normally in the nominative.

This is an equational sentence:

• That boy = my brother

So:

• Taj dečak is nominative
• moj brat is also nominative

That is why you get brat, not brata or bratom.

Serbian does not have definite or indefinite articles like English the and a/an.

So Serbian usually expresses definiteness through:

• context
• word order
• demonstratives such as taj = that

In this sentence, taj is a demonstrative, not an article. It specifically means that.

If you just said Dečak je moj brat, it could mean something like The boy is my brother or A boy is my brother, depending on context, though in real usage the context would usually make it clear.

Serbian word order is more flexible than English, but this sentence is the most neutral and natural order.

Taj dečak je moj brat is the standard way to say it.

Other orders are possible, but they change emphasis:

• Moj brat je taj dečak. = My brother is that boy.
• Taj dečak moj je brat. = more literary or strongly emphasized

So yes, Serbian allows movement, but the original sentence is the normal everyday order.

Je is a clitic, which means it tends to stand in a special position in the sentence, usually near the beginning of the clause rather than being stressed strongly.

In simple learner terms, you can think of je as naturally appearing after the first main chunk:

• Taj dečak | je | moj brat

You do not need to master clitic placement immediately, but it is useful to know that short forms like je often follow this pattern in Serbian.

A rough pronunciation guide:

• Taj ≈ tahy or tie
• dečak ≈ DEH-chak
• je ≈ yeh
• moj ≈ moy
• brat ≈ braht

A few key points:

• j is pronounced like English y in yes
• č is pronounced like ch in church
• Serbian spelling is quite phonetic, so words are usually pronounced close to how they are written

• taj = that
• ovaj = this

So:

• Taj dečak je moj brat. = That boy is my brother.
• Ovaj dečak je moj brat. = This boy is my brother.

This is a very common contrast in Serbian.

You replace je with nije:

Taj dečak nije moj brat.
= That boy is not my brother.

So:

• je = is
• nije = is not

Dečak specifically means boy.

If you want child, Serbian usually uses:

• dete = child

So:

• dečak = boy
• devojčica = girl
• dete = child

It is neutral and natural in both spoken and written Serbian. There is nothing especially formal or informal about it.

A Serbian speaker could easily use it in everyday conversation:

• Taj dečak je moj brat.

It is a perfectly standard sentence for learners to study.