“Sotto” può essere un avverbio, ma in “sotto il tavolo” diventa una preposizione.

It means sotto does not always do the same grammatical job.

• As an adverb, it stands on its own and means something like below / downstairs / underneath.
• As a preposition, it introduces a noun phrase and means under / beneath something.

So:

• Il gatto è sotto. = Here sotto is an adverb because it stands alone.
• Il gatto è sotto il tavolo. = Here sotto is a preposition because it is followed by il tavolo.

In other words, when sotto directly links to a noun, it is functioning as a preposition.

Because of what comes after it.

If sotto appears by itself, without a noun after it, it is usually an adverb:

• Guarda sotto. = Look underneath.

If sotto is followed by a noun phrase, it is a preposition:

• Guarda sotto il letto. = Look under the bed.

A useful shortcut is:

• no noun after it → probably adverb
• noun after it → preposition

Not literally. The sentence says diventa una preposizione because that is an easy way to explain its function in context.

A more precise grammatical way to say it would be:

• sotto can function as a preposition
• in sotto il tavolo, sotto is used as a preposition

So sotto is the same word, but its grammatical role changes depending on how it is used.

Because tavolo is a noun, and in Italian nouns often appear with an article.

• il tavolo = the table
• sotto il tavolo = under the table

The preposition sotto does not remove the article. It is simply followed by the noun phrase:

• sotto il tavolo
• sotto la sedia
• sotto i libri

This is different from some Italian prepositions such as a, di, da, in, su, which often combine with articles:

• a + il = al
• di + il = del
• su + il = sul

But sotto normally does not combine with the article in that way.

Not exactly in the traditional school grammar sense.

In Italian grammar, preposizioni semplici usually refers to a specific small set of core prepositions:

• di, a, da, in, con, su, per, tra, fra

Words like sotto, sopra, davanti, dietro can also function as prepositions, but they are often described separately because they are also adverbs in many contexts.

So yes, sotto can be a preposition, but it is not usually listed among the basic preposizioni semplici.

It can be followed by a pronoun, but usually with a different structure.

For example, Italian often uses di + pronoun after words like sotto:

• sotto di me = under me
• sotto di lui = under him

You may also hear expressions where sotto stands alone if the meaning is clear from context, but with stressed pronouns, di is common.

So sotto as a preposition is not limited to nouns like il tavolo. It can also introduce pronoun-based phrases.

Yes. That is exactly when sotto is acting as an adverb.

For example:

• Il gatto è sotto. = The cat is underneath.
• Abito sotto. = I live downstairs.
• Guarda sotto! = Look below!

In these cases, the location is understood from the context, so Italian does not need to repeat the noun.

Both can express the idea of under, but they are not always used in exactly the same way.

Very often, plain sotto is the most natural choice before a noun:

• sotto il tavolo
• sotto il ponte
• sotto la pioggia

You may also see sotto a, especially in some contexts or regional usage:

• sotto al tavolo
• sotto alla finestra

This is common and not wrong, but in many straightforward location phrases, learners are usually first taught sotto + article + noun:

• sotto il tavolo

So if you are unsure, sotto il tavolo is a very safe and standard choice.

Because sotto does not normally fuse with the article.

Italian has many contractions between certain prepositions and definite articles:

• a + il = al
• di + il = del
• in + il = nel
• su + il = sul

But sotto generally stays separate:

• sotto il tavolo
• sotto la sedia

So you should write it as two words: sotto il, not as one contracted form.

No. It often refers to physical position, but it can also be used more abstractly.

Physical:

• sotto il tavolo = under the table

Abstract or figurative:

• sotto pressione = under pressure
• sotto controllo = under control
• sotto accusa = under accusation
• sotto esame = under examination

In all these cases, the basic idea is still something like under or subject to.

Yes. Several Italian location words can work both as adverbs and as prepositions depending on whether they stand alone or introduce a noun phrase.

Common examples:

• sopra = above / over
• davanti = in front
• dietro = behind
• vicino = near
• lontano = far

Examples:

• Il libro è sopra. → adverb

• Il libro è sopra il tavolo. → preposition

• Lui è davanti. → adverb
• Lui è davanti alla porta. → preposition-like use

So sotto is part of a larger pattern in Italian.

Use this simple test:

Ask: Is there a noun phrase after it?

• If yes, it is functioning as a preposition.
  • sotto il tavolo
  • sotto la sedia
• If no, it is functioning as an adverb.
  • è sotto
  • guarda sotto

That is the easiest practical rule for learners.