SER & ESTAR
SER & ESTAR
BASIC USAGES (THE TROUBLESOME ONES):
The CID rule: SER is used to classify, identify, and define (CID) - three closely related terms, sometimes indistinguishable.
Examples:
Define:
Un avión es un vehículo con alas. ? An airplane is a vehicle with wings. (it could also be a classification)
Classify/Identify:
Mi amigo es mexicano ? My friend is Mexican
Este producto es muy peligroso ? This product is very dangerous.
Ese es mi hermano. ? That is my brother.
Mi anillo es de oro ? Mi ring is golden
Mi anillo es amarillo ? Mi ring is yellow
Mi anillo es bonito ? Mi ring is nice
Soy médico ? I am a doctor (don't say 'un doctor', unless you specify what makes you different from the rest of the doctors)
Mark es aburrido ? Mark is boring (classifying him as boring)
Joe es gordo ? Joe is fat (classified as a fat person)
La manzana es buena para la salud ? Apples are good for health (classification)
Notes:
' Nouns and pronouns are words used to define, identify and classify, so nouns go with SER.
' In Spanish we don't say 'I am 20 y.o.', but 'I have 20 years? (Tengo 20 años)
The verb ESTAR is used for situations and states in time and space.
Estoy aquí. ? I am here
Estoy bien ? I am well
Estoy cansado ? I am tired (this is not a classification: I am not a tired kind of person)
Mark está aburrido ? Mark is bored (not classifying him as a boring person)
Joe está gordo ? Joe is fat (he is not a kind of fat person. Last time I saw him, he was slim. Changes in time are considered here)
La manzana está buena ? The apple is good/tastes well (state experienced here and now)
Notes:
' nouns cannot be used with ESTAR. Do not say 'Estoy un doctor? o 'Estoy John Smith'.
' many adjectives have different meanings (in all languages), e.g. 'listo? means both 'smart? and 'ready'. The former is used to classify (and therefore, with SER), and 'listo? is used as a state (and therefore, with ESTAR).
' Marital status can go with either verb, but married and single are used more with ESTAR.
SPECIAL BASIC USES:
1) ESTAR + present participle ('gerundio') is used for progressive constructions:
Estoy comiendo ? I am eating
2) SER + past particple ('participio') is used for passive constructions indicating actions. These are not as common in Spanish as they are in English:
El puente será construido el año próximo ? The bridge will be built next year (by someone)
3) ESTAR + past participle ('participio') is used to indicate the result of an action:
La tienda está cerrada ? The shop is closed (result, not action: it is not closed or being by anyone, but already closed)
4) SER is used to tell time:
Es la una ? It is one (o'clock)
Son las dos ? It is two (o'clock)
5) Both SER and ESTAR can be used for dates, months and days of the week:
Hoy es 23 de febrero ? Today is February 23rd
Hoy es jueves ? Today is Thursday
Hoy estamos a 23 de febrero ? Today is February 23rd
Hoy estamos a jueves ? Today is Thursday
6) SER is used for prices (instead of 'costar'):
¿Cuánto es (todo)? ? How much is it(/everything)?
Son 30 dólares ? It is 30 dollars
OTHER: MISTAKES TO AVOID
Definitions and classifications are generally regarded as timeless and not restricted to any particular place. We don't say 'Water is a liquid... here and on Mondays only'. States and situations, on the other hand, are normally associated with places and moments.
For this reason, some books and pages say that SER is for permanent things, and ESTAR is for temporary things. Although this can relatively often be true, it is not advisable to use this pseudo-rule, because it is not a real rule, and it leads to constant confusions and contradictions. For example, the location of a place or an object can be either permanent (i.e. a building) or temporary (i.e. a book).
Mi abuelo está muerto ? My grandpa is dead (not exactly a temporary situation: he is not going to resucitate)
Nueva York está en los EE. UU. ? New York is in USA (A perfectly permanent situation)
Notice how the CID rule (identification/definition/classification) works in all the examples above.
The temporary/permanent fake rule leads to mistakes like these (both corrected):
Estoy Soy un estudiante ? I am a student (this is temporary: I graduate next week)
Jorge está es menor de eadad ? Jorge is underage (this is temporary: his 18th birthday is tomorrow)
Being a student and underage are regarded as classifications, because no moment or place is taken into account to make such statements, but they way we perceive them in our society (yes, this is subjective, of course). Particularly, 'un estudiante? is a noun, and nouns cannot go with ESTAR, since they are used to identify and classify things and people.
Do not use the temporary / permanent rule!
17 Answers
Natasha said:
Water might not be the best example to use here, because in scientific terms of course liquid is a state of matter. Or maybe the problem is with the word state . . . not sure . . .
Not really. As soon as you use "un", whatever follows becomes a noun, no matter what:
un comer
un sino
un para
The article turns any word into a noun, so it can be used to classify or define, and hence, it must be used with SER.
However, you can say:
El hierro está líquido
because here it is a state of matter, and an adjective. On top of that, we don't classify iron as being a liquid, do we? "El hierro es líquido" would be a plain wrong statement, as "líquido" is used as an adjective, and it would be a wrong classification.
We are not talking about the particular state of water here, now and under these circumstances, but classifying water through its main features. If it solidifies, it is called ice; if it melts, it is called steam.
MJ said:
Wonderful, Lazarus, thank you
and since both CID and ser have 3 letters, it will be easy to remember that the CID rule goes with ser and not estar.
I made up the "CID mnemonic rule" as I wrote the article, but what those three main uses are the ones recommended by the best (in my opinion) experienced and successful language teachers to explain the use of SER and ESTAR.
Natasha said:
Muy bien, espero que yo entiende. ¿Se puede decir lo siguiente? El agua es un líquido. El hielo es sólido, pero cuando se derrite, entonces está líquido.
"El hielo es un sólido." would be its definition (using a noun). "El hielo es sólido" would be a classification (according to its properties, through an adjective). "Está líquido" is correct, although scientists prefer to say "...está en estado líquido". I guess this proves the point that SER is not the opposite of ESTAR (like in temporary / permanent), but two different ways of portrait reality.
P.S. You better say "Espero haberlo entendido" (when you say "YO espero que YO entiendo", both subjects match, so you use infinitives instead of subjunctive)
This is a great reference article!!! Everyone should read this!!
I hope all this information will be in your book Lazarus!! 
A couple of minor points:
The shop is closed (result, not action: it is not closed or being closed by anyone, but already closed)
*The temporary/permanent fake rule leads to mistakes like these:
Estoy un estudiante ? I am a student (this is temporary: I graduate next week)
Jorge está menor de eadad ? Jorge is underage (this is temporary: his 18th birthday is tomorrow)*
You've announced that you were going to provide examples of mistakes. You might make it clearer, still, by adding something like "(should be) 'Soy un estudiante'" and "(should be) 'Jorge es menor de edad'".
This is one of the best that I have seen , if you know better please give the Link.
All members 'including me ' would be wise to study every word
that Lazarus has written here about Ser y estar, it is brilliant.
FANTASTIC! I can't wait to buy your book.
Thanks Laz,
For this reason, some books and pages say that SER is for permanent things, and ESTAR is for temporary things. Although this can relatively often be true, it is not advisable to use this pseudo-rule, because it is not a real rule, and it leads to constant confusions and contradictions. For example, the location of a place or an object can be either permanent (i.e. a building) or temporary (i.e. a book).
I actually in a louder voice than usual said O O O H H H!!! This is a little embarrassing and sad but hey, I like learning!! 
Lazarus, sometimes you amaze me and this is one of those times. Thank you for giving such well thought out answers.
lazarus1907 said:
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Lazarus said:
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Not really. As soon as you use "un", whatever follows becomes a noun, no matter what
Muy bien, espero que yo entiende. ¿Se puede decir lo siguiente?
El agua es un líquido. El hielo es sólido, pero cuando se derrite, entonces está líquido.
Estoy de acuerdo, si la película llega al nivel de los avances, ¡será fantástico! 
Daniel said:
FANTASTIC! I can't wait to buy your book.
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I hope it will be useful to move this thread to "vocabulary" as this comes up all the time.
Thanks again Laza
Muchas gracias, Lazarus. Es una excelente lección.
Wonderful, Lazarus, thank you and since both CID and ser have 3 letters, it will be easy to remember that the CID rule goes with ser and not estar.
This is outstanding, Lazarus! I wish we'd had it long ago!
Definitions and classifications are generally regardless as timeless and not restricted to any particular place. We don't say 'Water is a liquid... here and on Mondays only'. States and situations, on the other hand, are normally associated with places and moments.
Water might not be the best example to use here, because in scientific terms of course liquid is a state of matter. Or maybe the problem is with the word state . . . not sure . . .
