أعرف أولئك الناس.

أعرف means I know.

It comes from the verb عَرَفَ = to know / to recognize.
In this sentence, أعرف is the 1st person singular imperfect form, so it means I know.

A fully vowelled form would be أَعْرِفُ.

In Arabic, the verb itself usually shows the subject.

So أعرف already means I know, and you do not need to add أنا.

• أعرف أولئك الناس = I know those people
• أنا أعرف أولئك الناس = also possible, but أنا is added only for emphasis, contrast, or clarity

So the subject I is built into the verb.

أولئك means those.

It is a demonstrative used for plural nouns, usually referring to things or people that are relatively far from the speaker, or simply those in formal written Arabic.

So:

• هؤلاء = these
• أولئك = those

In this sentence, أولئك الناس means those people.

Because أولئك means those, while هؤلاء means these.

So the choice depends on meaning:

• هؤلاء الناس = these people
• أولئك الناس = those people

If the intended meaning is those people, then أولئك is the correct choice.

الناس means the people or simply people, depending on context.

In this sentence, together with أولئك, it means those people.

A useful point: الناس is very commonly used in Arabic to mean people in general or the people.

This is a very common question for English speakers.

In Arabic, when a noun comes after a demonstrative like this, that, these, or those, the noun is usually also definite.

So Arabic says:

• هذا الرجل = literally this the-man
• أولئك الناس = literally those the-people

That sounds unusual in English, but it is normal Arabic grammar.

So the الـ on الناس is correct and expected.

The sentence begins with the verb:

• أعرف = I know
• أولئك الناس = those people

So the structure is:

verb + object

This is a very normal Arabic pattern.

You could also say:

أنا أعرف أولئك الناس

but the shorter version أعرف أولئك الناس is perfectly natural because the verb already includes the subject I.

Yes.

In أعرف أولئك الناس, the thing being known is أولئك الناس = those people, so that phrase is the direct object of أعرف.

If full case endings were written, you would typically see:

أَعْرِفُ أُولَئِكَ النَّاسَ

Here:

• أعرفُ = verb
• أولئك = demonstrative within the object phrase
• الناسَ = object, so it takes the accusative in full formal grammar

In normal everyday writing, these endings are usually not written.

No, أولئك is generally treated as an indeclinable word in standard grammar, so its form stays the same.

That means whether it is part of the subject or the object, you still write:

أولئك

So in this sentence, even though the phrase is the object, أولئك does not change form.

It is pronounced an-nās, not al-nās.

That is because ن is a sun letter, so the l of الـ assimilates to the n sound.

So:

• written: الناس
• pronounced: an-nās

This is a very important pronunciation rule in Arabic.

A careful pronunciation would be:

aʿrifu ulāʾika an-nāsa

A more learner-friendly breakdown:

• أعرف = aʿrif
• أولئك = ulāʾika
• الناس = an-nās

So the full sentence is approximately:

aʿrif ulāʾika an-nās

If full case endings are pronounced in very formal reading, it would be closer to:

aʿrifu ulāʾika an-nāsa

It is a verbal sentence because it begins with a verb: أعرف.

In Arabic, a sentence that starts with a verb is called a verbal sentence, and a sentence that starts with a noun is called a nominal sentence.

So:

• أعرف أولئك الناس = verbal sentence
• أنا أعرف أولئك الناس still functions as a sentence with a verb, but it begins with a pronoun for emphasis

Yes, depending on context.

The verb عَرَفَ can mean:

• to know
• to recognize
• sometimes to be familiar with

So أعرف أولئك الناس could mean:

• I know those people
• I recognize those people

Usually the wider context tells you which meaning is intended.

Yes, it is completely natural and complete.

أعرف أولئك الناس has everything needed:

• a verb: أعرف
• an understood subject: I
• an object: أولئك الناس

So it is a full, correct sentence meaning I know those people.