Ser names what something is: identity, origin, material, the time. Estar names the state it is in: location, mood, condition, and every progressive tense.
Where the choice changes the meaning
| Context | ser | estar |
|---|---|---|
| Identity and role | Es profesora — a teacher by profession. | Está de profesora — working as a teacher for now. |
| Location | Only for events: la fiesta es en mi casa. | Está en el pasillo — where anything is. |
| Appearance | Es delgado — a thin person. | Está delgado — looks thin, or has lost weight. |
| Feelings | Es aburrido — a boring person. | Está aburrido — bored right now. |
| Time and date | Son las diez — every clock and calendar expression. | Not used. |
| Ongoing actions | Not used with the gerund. | Está hablando — every progressive tense. |
| Ready or clever | Es listo — clever. | Está listo — ready. |