How would you say "You must study more."?

Question

Would a correct answer to this also be ¿Se deben estudiar más?

Accepted Answer

Hola Gerald
As an impersonal sentence using "deber" we always use it in the singular: "Se debe estudiar más."
The plural "se deben..." can only be used if there was a subject that is plural, and that would be a passive construction, therefore you need agreement. For example, you can use the verb estudiar with a (passive) subject in plural:

Se deben estudiar los temas 3 y 4 concienzudamente. 
Topics 3 and 4 must be studied (=learnt) thoroughly.

With the impersonal "Se debe estudiar más" we are making a general statement as in "People in general should study more." ' you may see this sort of impersonal sentences translated in different ways, "one must...", "people should...", "you must...", with the latter using "you", not as a direct you, but as a general "you..."(impersonal).
See this other lesson to contrast it and make it more clear.
Saludos 
Inma

Answer

Mil gracias de nuevo.Una pregunta más, por favor:  If the "you" in the sentence "You must study more." refers to more than one person, that is, the third person plural, would the correct structure still be "se deben" or would it be better to go to a different construction altogether like "It's necessary that you..." or "You have to study more..."?In this case, the subject I suspect is no longer impersonal. ¿Verdad?

Answer

Hola Gerald
If you mean "You must study more" in an impersonal way as in "people in general should study more", it doesn't matter that you have a you, people... as the subject. As long as the nuance of your sentence is to refer to a general impersonal statement, you need the singular form "Se debe estudiar más". On the other hand, you could use a sentence that is directed to someone in particular (your listener, e.g your son who is in front of you) and use the subject again "you" in "you must study more", then you don't use an impersonal structure at all as that subject is specific, so you'd simply say "Debes estudiar más". The same for "it´s necessary that you (son) study more": es necesario que estudies más. 
I hope I understood correctly what you meant. 
Saludos

Answer

Thank you for the response. From your answer, then, I gather that if I had BOTH my son and daughter in front of me, the correct way to phrase it would be "Deben estudiar más." The "se" is omitted here because the sentence is now no longer impersonal, and the subject becomes the implied (plural) you. ¿Verdad?

Answer

Hola GeraldSí, exactamente. In that case you say "Deben estudiar más." in Latam, or "Debéis estudiar más." in Spain.

Answer

Dos mil gracias. Una úlitima pregunta.I'm trying to ascertain as accurately as I can, what my CEFR level is. From the previous Q and A entries that we've had, what level would you say this kind of discussion would qualify for, A2?, B1?, B2?.