May I sit here?
'Sedermi' — se-DER-mi. The reflexive pronoun 'mi' attaches to the infinitive when used with modal verbs.
Use this when a seat appears free but someone has placed a bag on it, or when you want to be polite before sitting next to someone on a crowded train.
'Sedermi' is the reflexive infinitive of 'sedersi' (to sit down) with the first-person pronoun attached. When a reflexive verb follows a modal like 'potere', the reflexive pronoun can attach to the infinitive or precede the modal: 'Posso sedermi' = 'Mi posso sedere'.
È libero questo posto?
Is this seat free?
The most common way to ask — preferred by most Italians.
C'è qualcuno qui?
Is someone here?
Asks whether the seat is taken without specifying your intention.
Le dispiace se mi siedo?
Do you mind if I sit down?
Very formal and polite; 'le dispiace' uses the formal 'Lei' pronoun.
Priority seats (posti riservati) marked with a blue or orange sticker are reserved for the elderly, pregnant women, and people with disabilities. Offering your seat in these situations is expected and socially enforced.