ser or estar: one rule, and where it stops working

English has one verb for this and Spanish has two, so there is no way to get it right by translating. You have to decide, every single time, and the decision is between two different questions about the same thing.

Ser answers what is it? Estar answers how is it, and where is it?

the rule, in one line

If you could put "is a" or "is the kind of thing that" in front of the English, you want ser. If you could put "is currently" or "is sitting", you want estar.

Mi hermano es alto — my brother is tall. That is what he is. Mi hermano está enfermo — my brother is ill. That is how he is today.

The version you were probably taught — permanent takes ser, temporary takes estar — is a useful shortcut for that same idea, and it is not the rule. It predicts está muerto wrongly, and being dead is about as permanent as things get. What is actually going on is that being dead is a state somebody ended up in, and states take estar however long they last.

Ser is what it is. Estar is how it is and where it is.

the forms

Both are irregular, both are among the most common verbs in Spanish, and both are worth being able to write out without thinking.

The accents on estar are not decoration. Esta with no accent is "this"; está is "he is". They are different words and an examiner reads them as different words.

what ser is for

Identity and description — who or what something is: Soy estudiante. Es mi hermana. Son españoles.

Origin, material, ownership, all with de: Soy de Inglaterra. Es de plástico. El libro es de María.

Time and dates — always ser, which surprises people, because a Tuesday is about as temporary as a thing can be: Son las tres. Hoy es martes. Es el veinte de mayo.

Impersonal statements: Es importante estudiar. Es difícil.

what estar is for

Where something is: Madrid está en España. Estoy en casa.

How somebody is — feelings, health, anything that could change by teatime: Estoy cansado. Está triste. Estamos preocupados.

Actions in progress, with the -ando / -iendo form: Estoy hablando. Está comiendo. This is the present continuous, and it is built on estar every time.

The result of something happening: La puerta está abierta. Someone opened it, and open is the state it is now in.

the exception worth memorising

Location takes estar — except for an event, which takes ser.

El museo está en el centro. The museum sits there. La fiesta es en mi casa. The party takes place there.

A museum is an object with a position. A party is not an object at all; it is something that happens, and saying where it happens is closer to saying when it happens. This turns up in exams more than its size deserves, so it is worth knowing rather than working out on the spot.

the adjectives that mean two things

This is the part that actually costs marks, because both versions are correct Spanish and only one of them is what you meant.

Estoy aburrido is "I am bored". Soy aburrido is "I am a boring person". You can see the pattern underneath: ser describes what the thing is like as a matter of course, and estar describes how it has turned out right now. Green is a colour a thing is; unripe is a stage a banana is at.

the feelings trap

If you take one thing from this post, take this one: feelings and moods go with estar.

Estoy triste — I am sad. Soy triste — I am a miserable person.

The same goes for contento, enfadado, nervioso, preocupado, cansado. They are all how you are, not what you are, and they all come up in speaking and writing tasks about school, family and free time — which is to say, constantly.

making it automatic

Ser and estar are not hard to understand. They are hard to do at speed, while you are also thinking about a tense, an adjective ending and what you actually want to say. The only thing that fixes that is meeting the choice often enough that it stops being a choice.

langrevise drills both verbs in every tense GCSE asks for, inside real sentences rather than as a table to stare at, and brings each one back just before you would have forgotten it.