Should v Must
How would you distinguish between should and must in Spanish ?
I use deber to be should, but it seems to be used more for must than should.
Does anyone have a definitive answer please.
Thank you.
According to my teacher.
debería estirarme cada dia ----- should.
debo tomar una pastilla para el corazón cada dia ------ must.
5 Answers
Your teacher is correct about the difference of the two words, but as Jubilado noticed, por a carazon is completely wrong (spelling and usage).
I've heard it said that deber in its present indicative form suggests a moral/ethical obligation, which makes sense since it literally means 'to owe (a debt)': te debo = I owe you.
However, as Jubilado says, rendering it in its conditional form lends it more of the sense of should in English. That said, should too has a moral/ethical overtone.
I would suggest tener que is more morally/ethically neutral, i.e. referring to something that you have to do as opposed to something that you're morally/ethically obliged to do.
However, when I did Pimsleur I found that the actors would use deber in its present indicative form much more than in its conditional form, even when there was no suggestion of strong compulsion (whereas Michel Thomas was clear that this is a relatively strong form).
I guess there's a wide variety of modes of expression, using different vocab and forms to put your point across... 
Yes could is conditional of poder, which in turn is the would form.
Podría traerme un vaso de agua, por favor - Would you bring me a glass of water, please.
(Tú) debes venir a la fiesta - you must come to the party.
(Tú) debieras/deberías venir a la fiesta - you should come to the party.
Would that help Tomásde Alba?
To my understanding could is expressed using the conditional form of poder.
¿Podría traerme un vaso de agua, por favor? – Could you bring me a glass of water please?
Podría haber sido un contendiente. Podría haber sido alguien. I could have been a contender. I could have been somebody. (Quote from the film On the Waterfront - Marlon Brando)
1st person singular and 3rd person singular are the same.
Tú debes venir a la fiesta. - You should come to the party.
Should is expressed using the verb deber but it also seems to get translated as must; however I have always used tener + que to say must or have to. Tengo que ir al banco. – I must/have to go to the bank. Tienen que cambiar trenes en Santander. – They must/have to change trains in Santander.
The use of the conditional for the verb deber softens the obligation from an imperative requirement. In the present indicatve debo the obligation is present and stronger. I find it difficult with all the modal implications in English to ascertain without a good deal of context exactly how strong the obligation is and where the responsibility lies. I think your teacher makes a good point in your 2 examples but the second one is poorly written. I think it should be Cada día debo tomar mi pastilla de corazón.
