El perro persigue la pelota.

Because perro is a masculine noun and pelota is a feminine noun.

In Spanish, nouns usually have grammatical gender, and the article has to match:

• el = masculine singular
• la = feminine singular

So:

• el perro
• la pelota

This is about grammatical gender, not necessarily real-world sex. A ball is not biologically female, but pelota is still grammatically feminine.

Persigue is the third-person singular present tense form of perseguir.

It matches subjects like:

• él
• ella
• usted
• or a singular noun like el perro

So in El perro persigue la pelota, the subject is el perro, and the verb has to be persigue.

A few present-tense forms of perseguir are:

• yo persigo
• tú persigues
• él/ella/usted persigue
• nosotros perseguimos
• vosotros perseguís (used in Spain)
• ellos/ellas/ustedes persiguen

Because perseguir is a stem-changing verb in the present tense.

The e in the stem changes to i in most forms:

• persigo
• persigues
• persigue
• perseguimos
• perseguís
• persiguen

Notice that nosotros and vosotros do not make the stem change:

• nosotros perseguimos
• vosotros perseguís

This kind of pattern is very common in Spanish.

Because Spanish often does not need subject pronouns.

The verb ending usually tells you who the subject is, and in this sentence the subject is already stated explicitly as el perro. So adding él would usually be unnecessary.

Natural Spanish:

• El perro persigue la pelota.

Less natural here:

• Él persigue la pelota. (only if the dog has already been mentioned and you want to say *he/it)*

Spanish uses subject pronouns mainly for:

• emphasis
• contrast
• avoiding ambiguity

This is the most neutral and common word order: Subject + Verb + Object.

• El perro = subject
• persigue = verb
• la pelota = direct object

Spanish is more flexible than English, so other orders are possible, but they usually change the emphasis:

• La pelota la persigue el perro. = The dog is the one chasing the ball. / As for the ball, the dog is chasing it.

For a simple, neutral sentence, El perro persigue la pelota is the best choice.

Because the Spanish present tense can often express what English says with either:

• chases
• is chasing

So El perro persigue la pelota can mean:

• The dog chases the ball (habitual/general)
• The dog is chasing the ball (happening now)

The exact meaning depends on context.

Spanish also has a progressive form:

• El perro está persiguiendo la pelota.

But Spanish uses the simple present more often than English does for actions happening right now.

Because Spanish normally uses articles much more than English.

With normal countable nouns like these, you generally need them:

• el perro
• la pelota

Leaving them out would sound incomplete or unnatural in a basic sentence.

Spanish often requires an article where English might not, especially with ordinary singular nouns that are specific or identifiable in context.

Because la pelota is a direct object, but it is not a person.

Spanish uses the personal a mainly before specific human direct objects, and sometimes animals if they are treated as individual beings with emotional importance.

Compare:

• Veo al profesor. = I see the teacher.
• Veo la pelota. = I see the ball.

So here:

• El perro persigue la pelota. ✅
• El perro persigue a la pelota. ❌

In gue and gui, the u is usually silent in Spanish.

So persigue is pronounced roughly like:

• per-SEE-gheh in much of Spain

The important part is that gui sounds like gi, not goo-ee.

If Spanish wants the u to be pronounced in this pattern, it uses a diaeresis:

• güe
• güi

For example:

• pingüino

But in persigue, there is no diaeresis, so the u is silent.

The stress falls on si:

• per-SI-gue

Why? Because it ends in a vowel, and Spanish words that end in a vowel, n, or s are normally stressed on the second-to-last syllable unless there is a written accent mark.

So:

• per-si-gue → stress on si

No written accent is needed because it already follows the normal stress rule.

Usually this specific sentence sounds like a particular dog and a particular ball:

• El perro persigue la pelota.

But depending on context, Spanish can use the definite article in more general statements too.

Still, if you wanted to clearly make it general as a class of thing, you might more often say something like:

• Los perros persiguen pelotas. = Dogs chase balls.
• El perro persigue pelotas. = The dog chases balls.

So in isolation, El perro persigue la pelota is most naturally understood as one specific dog chasing one specific ball.