Le professeur explique pourquoi ce verbe change au pluriel.

Le professeur means the teacher/professor is grammatically masculine here.

A few useful points:

• professeur is traditionally a masculine noun in standard French.
• For a male teacher, le professeur is the normal form.
• For a female teacher, modern French may use:
  • la professeure in many places
  • sometimes la professeur in more traditional usage

So in this sentence, le professeur tells you the teacher is being referred to as masculine, or simply that the masculine form is being used.

Explique is in the present tense.

It comes from the verb expliquer = to explain.

Here is the breakdown:

• j’explique = I explain
• tu expliques = you explain
• il/elle explique = he/she explains

Since the subject is Le professeur, the verb takes the il/elle form: explique.

In English, you might say The teacher explains why this verb changes in the plural, without that, or sometimes explains that this verb changes... depending on the structure.

In French, pourquoi introduces the idea directly:

• Le professeur explique pourquoi... = The teacher explains why...

You do not need que before pourquoi here.
So French naturally says:

• explique pourquoi ce verbe change...

not

• explique que pourquoi... ❌

Because this is an indirect question, not a direct question.

Compare:

• Direct question: Pourquoi ce verbe change-t-il ?
• Indirect question: Le professeur explique pourquoi ce verbe change.

In an indirect question, French usually keeps normal statement word order:

• pourquoi ce verbe change

not inverted order.

This is similar to English:

• Direct: Why does this verb change?
• Indirect: The teacher explains why this verb changes.

English changes word order too, and French does the same in its own way.

Because verbe starts with a consonant sound.

French uses:

• ce before masculine singular nouns starting with a consonant
  
  • ce livre
  • ce verbe
• cet before masculine singular nouns starting with a vowel or mute h
  
  • cet ami
  • cet homme

So:

• ce verbe ✅
• cet verbe ❌

Ce is a demonstrative adjective. It means this or that, depending on context.

So ce verbe means:

• this verb
• sometimes that verb, if the context points to something farther away or previously mentioned

French does not always distinguish this and that as clearly as English does.
If French wants to be more explicit, it can say:

• ce verbe-ci = this verb
• ce verbe-là = that verb

But in your sentence, simple ce verbe is completely normal.

Because the subject is ce verbe, which is singular.

The verb changer in the present tense goes like this:

• je change
• tu changes
• il/elle/on change
• nous changeons
• vous changez
• ils/elles changent

Here, ce verbe = this verb, which is singular, so French uses:

• ce verbe change

Even though the sentence mentions au pluriel, the subject is still one verb, not several verbs.

The usual French expression is au pluriel = in the plural.

It is built from:

• à + le = au

So:

• au pluriel literally looks like to the plural, but idiomatically it means in the plural

This is just the normal fixed expression.
French commonly says:

• un mot au singulier
• un mot au pluriel

not usually en pluriel in this context.

Because pluriel here is a noun, not an adjective describing several things.

In au pluriel, French is talking about the plural form/category/system as one concept.

So it is singular because it means something like:

• in the plural form
• in the plural

The same happens with:

• au singulier = in the singular

Even though plural refers to more than one item, the word pluriel itself is singular in this expression.

Yes. Pourquoi means why, and it introduces an indirect question.

In this sentence, the teacher is explaining why something happens:

• pourquoi ce verbe change au pluriel

So pourquoi is still the word why, but it is embedded inside a larger sentence instead of standing alone as a direct question.

A simple pronunciation guide is:

luh proh-feh-suhr ex-pleek poor-kwah suh vehrb shahnzh oh ploo-ree-el

A few helpful pronunciation notes:

• le is usually a light luh
• professeur has stress spread evenly; French does not stress words as strongly as English
• explique ends with a clear -k sound
• pourquoi sounds roughly like poor-kwah
• ce here sounds like suh
• verbe ends with a sounded b
• change ends with a soft zh sound, like the s in measure
• au sounds like oh
• in natural speech, le professeur explique may flow together smoothly

The sentence breaks down like this:

• Le professeur = subject
• explique = main verb
• pourquoi ce verbe change au pluriel = what is being explained

Inside that last part:

• pourquoi = why
• ce verbe = subject of the embedded clause
• change = verb
• au pluriel = expression meaning in the plural

So the structure is:

[Subject] + [main verb] + [indirect question clause]

That is a very common and useful French pattern.