هو يقسم أن هذا حقيقي.

Because Arabic often allows an explicit subject pronoun even when the verb already shows the person.

• يقسم by itself already tells you the subject is he
• هو can be added for:
  • emphasis
  • contrast
  • clarity

So both of these can work:

• هو يقسم أن هذا حقيقي
• يقسم أن هذا حقيقي

The version with هو feels a bit more explicit: He swears that this is true.

Here, يقسم means he swears or he takes an oath.

That said, the same unvoweled spelling يقسم can also mean he divides, depending on context and pronunciation.

So context is very important:

• يُقْسِمُ = he swears
• يَقْسِمُ = he divides

In your sentence, because of the meaning and the clause after it, it clearly means he swears.

In this sentence, the verb is from أقسمَ which means to swear.

So:

• past tense: أقسمَ = he swore
• present tense: يُقسمُ = he swears / is swearing

This is different from قَسَمَ / يَقْسِمُ meaning to divide.

Here أن means that and introduces the content of the oath:

• هو يقسم = he swears
• أن هذا حقيقي = that this is true

So the whole sentence structure is:

• main clause: هو يقسم
• subordinate clause: أن هذا حقيقي

A more grammatical way to think about it is that أنّ introduces a clause functioning as the object or complement of يقسم.

Here, the correct fully vowelled form is أَنَّ with a shadda on ن.

Why?

Because this is anna, the particle meaning that, used before a noun clause:

• أَنَّ هذا حقيقي = that this is true

This is different from أَنْ (an), which is used before a present-tense verb, as in:

• أريد أن أذهب = I want to go

In normal Arabic writing, short vowels and shadda are usually omitted, so both may appear simply as أن in plain text. But in your sentence, the intended form is أَنَّ.

هذا means this.

In this sentence, it refers to this thing / this claim / this matter being discussed. Arabic often uses هذا in a broad, abstract way, just like English this.

So أن هذا حقيقي means:

• that this is real
• that this is true

depending on context.

This is a very common learner question.

هذا is pronounced hādhā. The long ā after the h is part of the word, even though the spelling is somewhat irregular.

In fully marked text, you may sometimes see:

• هٰذا

That little dagger alif shows the long ā sound. But in normal writing, Arabic usually writes it simply as:

• هذا

So you just have to learn this word as a common spelling-pronunciation pair.

Because it agrees with هذا, which is masculine singular.

Arabic adjectives agree with the noun or pronoun they describe in gender and number.

So here:

• هذا = masculine singular
• حقيقي = masculine singular

If it were feminine, you would expect something like:

• هذه حقيقية = this is true/real for a feminine referent

Yes. حقيقي is an adjective meaning real, genuine, or true depending on context.

In this sentence it works as the predicate of هذا, so:

• هذا حقيقي = this is real / this is true

A very common alternative would be صحيح:

• هذا صحيح = this is correct / true

The difference is roughly:

• حقيقي leans toward real, genuine, actual
• صحيح leans toward correct, true

But in many contexts, both can be translated as true.

A fully vowelled version would be:

هُوَ يُقْسِمُ أَنَّ هٰذَا حَقِيقِيٌّ

Word by word:

• هُوَ = huwa
• يُقْسِمُ = yuqsimu
• أَنَّ = anna
• هٰذَا = hādhā
• حَقِيقِيٌّ = ḥaqīqiyyun

In normal everyday writing, most of these vowels are omitted.

This sentence is natural, but Arabic does allow some flexibility.

Common possibilities include:

• هو يقسم أن هذا حقيقي
• يقسم أن هذا حقيقي

Both are normal.

The first is more explicit because it includes هو. The second is a little more streamlined because the verb already tells you the subject is he.

For a learner, the given sentence is a perfectly good standard model to follow.