هو ينتسب إلى المكتبة.

ينتسب إلى means to belong to, to be affiliated with, or to be associated with.

It is a fairly formal expression. It is often used for affiliation with:

• a family or lineage
• a tribe
• an organization
• an institution

So هو ينتسب إلى المكتبة means that he is affiliated with the library, not just physically going there.

Because Arabic often allows the subject pronoun to be either:

• included for emphasis, contrast, or clarity
• left out when the verb already makes it clear

So both are possible:

• هو ينتسب إلى المكتبة
• ينتسب إلى المكتبة

The verb ينتسب already shows third person masculine singular, so هو is not strictly necessary.

The root is ن س ب.

This root is connected with ideas like:

• relation
• lineage
• connection
• attribution

The verb ينتسب comes from the past tense انتسب and is from Form VIII.

A helpful way to think of it is:

• basic root idea: connection or relation
• انتسب / ينتسب: to affiliate oneself, to belong, to claim connection with

Because انتسب normally takes إلى to show the group or institution someone belongs to.

So:

• ينتسب إلى المكتبة = he belongs/is affiliated to the library

This is similar to English belong to, where the idea is not a direct object, but a relationship marked by a preposition.

After a preposition like إلى, the noun is in the genitive case.

So in fully vocalized Arabic, it would be:

هو ينتسب إلى المكتبةِ

The final kasra on المكتبةِ shows the genitive. In normal everyday writing, short vowels are usually not written, so you just see المكتبة.

It is pronounced al-maktaba.

That is because م is a moon letter, so the ل in ال is pronounced clearly.

So:

• المكتبة = al-maktaba
• not am-maktaba

In full careful pronunciation of the whole sentence, you could say:

huwa yantasibu ilā al-maktabati

In pause, the final case vowel is often dropped in speech:

• al-maktaba

ينتسب is in the imperfect form.

In Modern Standard Arabic, the imperfect can express:

• present
• habitual action
• sometimes future, depending on context

Here it most naturally means a present or general state:

• he belongs to
• he is affiliated with

It is grammatical, but it sounds somewhat formal and institutional.

ينتسب إلى often suggests official affiliation, not just ordinary membership.

If you mean simple library membership, Arabic may more naturally use something like:

• هو عضو في المكتبة = he is a member of the library
• لديه عضوية في المكتبة = he has a membership in the library

So هو ينتسب إلى المكتبة works best when you want the idea of formal affiliation.

Yes. You can also say:

ينتسب إلى المكتبة

This is very natural in Arabic.

Starting with هو gives a slightly stronger sense of:

• topic marking
• emphasis
• contrast

For example, it can feel like:

• He is affiliated with the library

So both are correct, but هو adds a little extra focus.