هو يصف الأعراض.

• هو = the subject pronoun, he
• يصف = the verb, describes / is describing
• الأعراض = the direct object, the symptoms

So the structure is:

subject + verb + object

Even though Arabic often starts sentences with a verb, this sentence begins with the pronoun هو, which makes it a nominal sentence followed by a verbal idea.

Yes, Arabic can say just يصف الأعراض.

That is because the verb يصف already tells you the subject is he through its form. So:

• يصف الأعراض = He describes the symptoms
• هو يصف الأعراض = He is describing the symptoms / He describes the symptoms

Adding هو can make the subject more explicit. It may be used:

• for clarity
• for emphasis
• for contrast, such as He describes the symptoms, not someone else

So هو is often optional here.

In Modern Standard Arabic, verbs change form depending on the subject.

يصف is a present-tense verb form used with:

• he
• sometimes also it in translation, depending on context

The يـ at the beginning is a common marker of the 3rd person masculine singular in the present tense.

So:

• هو يصف = he describes
• هي تصف = she describes
• أنا أصف = I describe

It can mean either, depending on context.

In Arabic, the present tense often covers both:

• simple present: he describes
• present continuous: he is describing

So هو يصف الأعراض could be understood as either one. Context tells you which English translation is best.

The root is و ص ف.

This root is connected with the idea of:

• describing
• characterization
• giving a description

A few related words are:

• وصف = description / he described, depending on context
• صفة = attribute, adjective, characteristic
• يوصف = is described

Recognizing roots is very helpful in Arabic because many related words come from the same three-consonant root.

ال is the Arabic definite article, meaning the.

So:

• أعراض = symptoms
• الأعراض = the symptoms

This tells us the speaker means specific symptoms, not symptoms in general.

الأعراض is a plural noun. Its singular is usually عَرَض in the medical sense of symptom.

So:

• عَرَض = symptom
• أعراض = symptoms
• الأعراض = the symptoms

This is a broken plural, which means the plural is formed by changing the internal pattern of the word, not just adding an ending.

In fully vowelled formal Arabic, the direct object would normally be in the accusative case:

• الأعراضَ

That final fatḥa shows it is the object of the verb.

However, in most everyday printed Arabic, short vowels and case endings are usually not written. So you will often see simply:

• هو يصف الأعراض

without the final case marking.

Yes. It is natural, but it is not the only possibility.

Arabic commonly allows both:

• هو يصف الأعراض = He describes the symptoms
• يصف الأعراض = He describes the symptoms
• يصف هو الأعراض = possible, but less neutral in many contexts

Also, Arabic often likes verb-first order, especially in plain narration. But starting with هو is perfectly correct when the speaker wants to mention or emphasize the subject.

You would change both the pronoun and the verb form:

• هي تصف الأعراض

Here:

• هي = she
• تصف = she describes

So the verb must agree with the subject in person and gender.

A common Modern Standard Arabic negation is:

• هو لا يصف الأعراض

This means He does not describe the symptoms or He is not describing the symptoms, depending on context.

Here:

• لا negates the present tense verb
• يصف stays in the present form

So the pattern is:

هو + لا + verb + object

Yes, here you pronounce the l in ال clearly, because أعراض begins with أ and not with a sun letter.

So it is pronounced roughly:

• huwa yaṣifu al-aʿrāḍa in full formal pronunciation

The ال stays al-, not assimilated.

For comparison, with a sun letter, the l would assimilate, but that does not happen here.