Learn Hardcore Italian: Metto la tazza su un sottobicchiere di legno.

Italian is a “pro-drop” language, which means that subject pronouns are often omitted because the verb ending itself indicates who is performing the action. The -o ending in metto already tells you it’s first-person singular (“I put”), so adding io (I) is unnecessary unless you want extra emphasis.

Why do we say la tazza (definite) but un sottobicchiere (indefinite)?

We use the definite article la before tazza because we’re referring to a specific cup—perhaps one both speaker and listener know about. By contrast, un sottobicchiere introduces the coaster for the first time and it doesn’t matter which one it is, so we use the indefinite article un (“a”).

Is sottobicchiere one word or two, and why?

It’s written as a single compound noun: sottobicchiere. Many Italian nouns formed by a preposition (sotto) + another noun (bicchiere) become one word. Writing them together reflects that they function as a single lexical item meaning “coaster.”

Why is the article un and not uno before sottobicchiere?

Italian uses uno before masculine nouns starting with s + consonant (like scoiattolo), z, gn, ps, x or y, because those clusters are harder to pronounce. Sottobicchiere begins with s+o (s + vowel), so the regular form un is correct.

Why do we say di legno instead of in legno, and is there a difference?

Both di legno and in legno can mean “made of wood,” but di legno is the most common way to state material composition in Italian. In legno is also correct and perhaps more literary, but you’ll see di + material used far more often in everyday speech.

What’s the difference between the prepositions su and sopra here?

Su and sopra are virtually interchangeable when you mean “on” or “above.” Su is shorter and very common; sopra can add a shade of emphasis or be used in fixed expressions (e.g. sopra il tavolo). In this sentence you could say either su un sottobicchiere or sopra un sottobicchiere without changing the basic meaning.

Could we contract su un into sul here, like we do with su + il = sul?

No. Contractions only occur with definite articles:

su + il = sul
su + lo = sullo
su + la = sulla
Indefinite articles (un, una) never contract with prepositions, so you must keep su un intact.