su

Su is the third-person singular (and formal second-person singular usted) possessive determiner. Unlike English, which distinguishes "his," "her," and "its," Spanish uses the single form su for all three, plus formal "your" and "their" when the plural is su (before a singular noun) or sus (before a plural noun).

This ambiguity is a genuine structural feature, not a pitfall to fix. In conversation, context clarifies the possessor. When disambiguation is needed, Spanish uses a prepositional phrase: "el coche de él" (his car) versus "el coche de ella" (her car). Learners often over-construct these phrases when su alone would sound natural.