Nadharia hii ni mpya.

A simple breakdown is:

• nadharia = theory
• hii = this
• ni = is / are
• mpya = new

So the structure is literally something like:

• theory this is new

Swahili often orders things differently from English, even when the meaning is straightforward.

In Swahili, demonstratives like this and that usually come after the noun.

So:

• nadharia hii = this theory
• literally: theory this

This is normal Swahili word order. English says this theory, but Swahili says theory this.

Ni is the copula, the word that links the subject with what is being said about it. In English, this is usually is, am, or are.

So in:

• Nadharia hii ni mpya

ni connects nadharia hii (this theory) with mpya (new).

It works like is here.

Yes, adjectives in Swahili often agree with the noun class of the noun they describe.

Nadharia belongs to the N class (often called class 9/10). With this class, the adjective -pya appears as mpya.

So:

• nadharia mpya = a new theory
• Nadharia hii ni mpya = This theory is new

The form mpya is the correct agreeing form here.

Nadharia is normally treated as a class 9 noun in the singular, with a plural in class 10. In practice, the noun form often stays the same in both singular and plural.

This matters because noun class affects things like:

• demonstratives
• adjectives
• verbs
• pronouns

For example:

• singular: nadharia hii = this theory
• plural: nadharia hizi = these theories

The noun itself may stay nadharia, but the agreeing word changes from hii to hizi.

You would say:

• Nadharia hizi ni mpya.

Here is what changed:

• hii → hizi because the noun is now plural

Notice that:

• nadharia stays the same
• mpya also stays the same here

So:

• Nadharia hizi ni mpya = These theories are new

In this sentence, you should not leave it out if you want a full sentence meaning This theory is new.

• Nadharia hii ni mpya. = This theory is new.

If you say:

• nadharia hii mpya

that sounds more like this new theory, which is a noun phrase, not a complete sentence.

So ni is important here because it turns the phrase into a full statement.

Yes. Nadharia hii is a complete noun phrase meaning:

• this theory

It can be used inside a larger sentence, for example:

• Nadharia hii ni muhimu. = This theory is important.
• Ninaelewa nadharia hii. = I understand this theory.

So in your sentence, nadharia hii is the subject.

Hii is usually pronounced something like hee-ee.

A helpful way to think of it:

• hii has two i vowels
• both are pronounced clearly

So do not reduce it to a short English-style hee. Keep both vowels audible.

In nadharia, the dh represents a sound like the th in English this or that.

A rough pronunciation guide is:

• na-dha-ri-a

The vowels are usually pronounced clearly:

• na
• dha
• ri
• a

So try not to blur the vowels together too much.

The normal, neutral order is:

• Nadharia hii ni mpya.

That is the standard way to say This theory is new.

Swahili can sometimes move elements around for emphasis in certain contexts, but for a learner, the best pattern to remember is:

• noun + demonstrative + ni + adjective

So this sentence is a very useful model:

• kitabu hiki ni kipya = this book is new
• gari hili ni jipya = this car is new
• nadharia hii ni mpya = this theory is new