Nadie vio al monstruo.

Nadie means no one or nobody.

In this sentence, nadie is the subject:

• Nadie = no one
• vio = saw
• al monstruo = the monster

So grammatically, it is literally No one saw the monster.

Because in Spanish, when a negative word like nadie, nunca, or nada comes before the verb, you do not add no.

So:

• Nadie vio al monstruo. = No one saw the monster.

But if nadie comes after the verb, then you do need no:

• No vio nadie al monstruo. = No one saw the monster.

This is a very common Spanish pattern:

• Nadie vino. = No one came.
• Nada pasó. = Nothing happened.
• Nunca fui. = I never went.

Vio is the third-person singular preterite form of ver (to see).

So it means:

• he/she saw
• you saw (formal usted)
• it saw

In this sentence, the subject is nadie, which is grammatically treated as third-person singular, so vio is the correct form.

Because ver is irregular in the preterite.

Its preterite forms are:

• vi = I saw
• viste = you saw
• vio = he/she/it saw
• vimos = we saw
• visteis = you all saw
• vieron = they saw

So vio is simply the correct preterite form of ver.
It does not keep the stem ve- in the preterite.

This is because of the personal a.

In Spanish, when the direct object is a specific person or something treated like a person, Spanish often uses a before it.

Here, monstruo is not a human, but it is being treated as a specific, animate being, so a is used:

• vio al monstruo = saw the monster

Also, a + el = al, so:

• a el monstruo becomes al monstruo

This contraction is mandatory.

Yes.

Al is the contraction of:

• a
  • el = al

For example:

• Voy al parque. = I’m going to the park.
• Vio al monstruo. = He/She saw the monster.

This only happens with a + el.
It does not happen with feminine articles:

• a la niña
• a la casa

Because the noun is el monstruo.

Many Spanish nouns ending in -o are masculine, and monstruo is one of them:

• el monstruo

So when it combines with a, you get:

• al monstruo

If the noun were feminine, you would use a la instead:

• vio a la criatura

Yes.

In Nadie vio al monstruo:

• Nadie = subject
• vio = verb
• al monstruo = direct object

You can test this by asking:

• What did no one see?
• The monster

That makes el monstruo the direct object.

Because nadie is grammatically singular in Spanish.

Even though it means no person / not anybody, it takes a singular verb:

• Nadie vino.
• Nadie sabe.
• Nadie vio al monstruo.

So vio is singular because nadie is singular.

Yes, Spanish allows more flexibility with word order.

The most neutral version is:

• Nadie vio al monstruo.

But other versions are possible for emphasis, for example:

• Al monstruo no lo vio nadie.

This also means No one saw the monster, but it puts special emphasis on the monster.

That version includes:

• al monstruo for emphasis at the front
• no
• lo as a direct object pronoun
• nadie later in the sentence

A learner should treat Nadie vio al monstruo as the basic, straightforward version.

Usually, no.

Nadie is the normal word for no one / nobody when talking about people:

• Nadie vio al monstruo.

Ninguno usually means none / not one, and it normally refers back to a group already mentioned:

• Había tres testigos, pero ninguno vio al monstruo. = There were three witnesses, but none of them saw the monster.

So for a simple sentence meaning No one saw the monster, nadie is the natural choice.

A rough pronunciation for a native English speaker is:

NAH-dyeh VYOH al mon-STROO-oh

A few helpful notes:

• nadie has two syllables after the d sound: na-die
• vio is usually one syllable: vyoh
• monstruo is often pronounced as two or three syllables depending on speed, but roughly mons-troo-o

In Spain, the v in vio sounds like a soft b/v sound, not a strong English v.

The preterite vio presents the action as a completed event:

• No one saw the monster as a finished fact

If you used the imperfect veía, the meaning would change and sound more like an ongoing or habitual situation:

• Nadie veía al monstruo = No one was seeing the monster / No one could see the monster

So vio is the natural form if you mean a completed past event.