Q1: Why does the "sé" in "no sé" require an accent mark?
A1: Spanish uses the diacritical accent mark (tilde diacrítica) to distinguish between monosyllabic homophones that serve different grammatical roles. The accented sé is the conjugated form of the verb saber (to know) or ser (to be, imperative). The unaccented se is a third-person reflexive or indirect object pronoun, as seen in se cayó (it fell).
Q2: Is saying "yo no sé" considered grammatically incorrect?
A2: It is grammatically correct, but pragmatic usage makes it redundant. Because the verb form sé applies exclusively to the first-person singular, native speakers omit yo unless they want to emphasize contrast between themselves and someone else.
Q3: How do I say "I don't know" politely to a customer or stranger?
A3: Avoid a flat no sé. Instead, use no sabría decirle (formal) or desconozco la respuesta, permítame averiguarlo ("I am unaware of the answer, allow me to look into it"). These phrases soften the interaction and maintain professional courtesy.
