Učlaniće se pod uslovom da potpiše obrazac.

Učlaniće se is the future form of učlaniti se, a verb meaning to join or more literally to become a member.

The se is a reflexive particle. In this verb, it is part of the normal dictionary form: učlaniti se. It does not mean himself/herself in a literal English sense here. Many Serbian verbs simply use se as part of the verb.

So:

• učlaniti se = to join / to become a member
• učlaniće se = he/she/it will join

This is how the future tense is often written in Serbian when the future particle će is attached directly to the infinitive.

Compare:

• učlaniti = infinitive
• on će se učlaniti = he will join
• učlaniće se = will join / he-she will join

When će comes after the infinitive directly, the infinitive usually drops -ti and combines with će:

• raditi → radiće
• potpisati → potpisaće
• učlaniti → učlaniće

So učlaniće se is a normal contracted future form.

Because in modern Serbian, da + present tense is very commonly used where English might use an infinitive or a subordinate clause.

After expressions like pod uslovom da (on condition that / provided that), Serbian requires a finite verb form, not an infinitive.

So:

• pod uslovom da potpiše obrazac = on condition that he/she signs the form

But:

• pod uslovom da potpisati obrazac = incorrect

This is very normal Serbian structure.

This is mainly about aspect.

• potpisati = perfective, meaning to sign as a completed act
• potpisivati / potpisuje = imperfective, meaning to be signing, to sign repeatedly, or to sign in a general/ongoing sense

Here the signing is a single completed condition. The person will join only if they complete the act of signing the form. That is why Serbian uses the perfective present form:

• da potpiše = that he/she sign, that he/she completes the signing

Using potpisuje would sound more ongoing or habitual, which does not fit as well here.

That is normal in Serbian subordinate clauses.

After words like da, especially in conditional, purpose, or dependent clauses, Serbian often uses a present-tense form to refer to a future action.

So even though potpiše is morphologically a present form, in this sentence it refers to a future event:

• pod uslovom da potpiše obrazac = provided that he/she signs the form

This is especially common with perfective present forms, which often refer to future completion in subordinate clauses.

Pod uslovom da means:

• provided that
• on condition that
• as long as

Yes, it is somewhat more formal or official-sounding than a simple ako (if).

So this sentence has a slightly formal or administrative tone, which fits well with words like učlaniti se and obrazac.

Often yes, but the nuance changes a little.

• Ako potpiše obrazac, učlaniće se. = If he/she signs the form, he/she will join.
• Učlaniće se pod uslovom da potpiše obrazac. = He/she will join provided that he/she signs the form.

Ako is the basic everyday word for if.

Pod uslovom da is more explicit and restrictive: it emphasizes that this is a required condition.

So both can work, but pod uslovom da sounds more formal and precise.

Because the preposition pod here requires the instrumental case.

The noun is:

• uslov = condition

In the instrumental singular, it becomes:

• uslovom

So:

• pod uslovom = under the condition / on condition

This whole phrase is a fixed expression, so it is best to learn it as a chunk:

• pod uslovom da = provided that

Obrazac is the direct object of potpiše, so it is in the accusative case.

The noun is masculine inanimate:

• nominative singular: obrazac
• accusative singular: obrazac

For many masculine inanimate nouns in Serbian, nominative and accusative singular look the same. That is why the form does not change here.

Yes. Serbian word order is fairly flexible.

You could also say:

• Pod uslovom da potpiše obrazac, učlaniće se.

This means the same thing, but it puts the condition first for emphasis.

The original version:

• Učlaniće se pod uslovom da potpiše obrazac.

starts with the main action and then adds the condition.

Both are natural.

No explicit subject is stated in the sentence.

Serbian often leaves out subject pronouns when the verb ending already shows the person and number. Here:

• učlaniće se = he/she/it will join

So the subject is understood from context. In English, you usually need a subject like he, she, or they, but Serbian often does not.

If needed, Serbian could make it explicit:

• On će se učlaniti pod uslovom da potpiše obrazac. = He will join provided that he signs the form.
• Ona će se učlaniti pod uslovom da potpiše obrazac. = She will join provided that she signs the form.