Why was the imperfect used here?
¡Hola a todos!
These two examples in the imperfect are driving me crazy!! they look pretty easy, but l just can't understand them!
+ No querer :-
María no quiso comprar la casa. = Maria refused to buy the house.
Juan no quería comprar la casa. = Juan did not want to buy the house. (imperfect??!)
l thought that ''refused'' has the same meaning as ''didn't want!'' then why was the imperfect used in the second example?
+ Saber :-
- Juan sabía que María venía. = Juan knew that Maria was coming.
l have no idea about this one!! l can't even understand it! is it the imperfect because he never stopped knowing? and how is ''venía'' used to mean ''was coming''?
Any help is very appreciated, thank you so much 
5 Answers
Remember that the preterite generally tells you "what happened" and the imperfect tends to indicate background information, "just the way things were" what was customary or habitual, or what was happening".
When faced with a sentence in the past, if you ask yourself "what happened" vs. "what was happening, what was the background situation, what was habitual", it usually clears up.
For example:
"The clock struck noon" vs. "It was noon". If you ask yourself which sentence answers "what happened", it is obviously the first one. "Dio las doce" (preterite). On the other hand, the second sentence just tells you the way things were, or the background information; nothing specific happened. "Eran las doce".
Going to your specific questions:
"She refused to buy the house" vs. "She didn't want to buy the house". In the first sentence, something definitely happened. There was a mental action of refusal. "No quiso comprar la casa." On the other hand, "She didn't want to buy the house" does not indicate that anything happened. People can want or not want to do things all the time, but they don't necessarily act on it. "No quería comprar la casa."
Likewise "quiso" vs. "quería" shows the difference between an action vs. a non action. "Quiso levantalo" means "He tried to lift it." Can you see in your mind someone trying very hard to life a large box or a very heavy weight? "Quería levantarlo" means "He wanted to lift it." Can you see that there is no action there; can you picture him just standing there' looking at the box or the large weight?
Let's take "supo" vs. "sabía". Since "supo" is in the preterite, you know that it must somehow indicate that something happened. "Supo" means "he found out" or "he realized" something. Can you see that this is a mental action? "Supo la verdad" - "He found out the truth". Can you picture the look on his face as he realized or found out something? Can you see that he found out that he had won a million euros or that this child was really his son? On the other hand "Sabía la verdad" - "He knew the truth". There is no action there; it's just the way things were. For example, he knew that this child was his son.
Lastly, your question about "venía": Remember that one of the translations for imperfect is "was -ing". Therefore "ella venía a mi casa" can be translated as "she was coming to my house".
Therefore, "Sabía que venía a mi casa": is translated that "He knew that she was coming to my house".
I apologize if this post is wordy or lengthy, but I have found in teaching this concept for several decades that it is useful to use "what happened" for the preterite vs. "what was the background, what was happening, what was customary" for the imperfect.
Those verbs mean differently in the preterite and imperfect.
"Juan no quería" means he didn't want to, but perhaps he might have ended up buying it. "No quiso" means he didn't flatly want to and so he didn't, his "not wanting" came to an end.
"Juan supo que..." would be more like he "found out" or "came to know", like a sudden knowledge or realization of something.
l thought that ''refused'' has the same meaning as ''didn't want!''
refuse
2 : to say or show that you are not willing to do something that someone wants you to do
That is exactly what "refuse" means!
...then why was the imperfect used in the second example?
The question would be why is preterite used in the first one. Go back in time and revive the moment. How would you describe it from within, at that very moment? Simple:
María no quiere comprar la casa.
(Still in the past) Is she going to buy the house? I don't know, we'll see. (No back to the present) If you required present tense then, you require imperfect now, because imperfect is a mental present. So, why preterite? Preterite does not send you back to the moment, but you contemplate the entire event once finished, so with "no quiso" we know that she didn't want to buy the house... until the end; she was determined not to buy it, and didn't buy it. Now we know the outcome.
Juan sabía que María venía. = Juan knew that Maria was coming.
l have no idea about this one!! l can't even understand it! is it the imperfect because he never stopped knowing? and how is ''venía'' used to mean ''was coming''?
Whether he stopped knowing or not is not provided by imperfect. Let's go back in time and let's revive that moment when Juan knew María was coming. How would you describe it?
Juan sabe que María viene.
The same thing is described with imperfect now, because that's how we recall things from our memories.
*There are some verbs that change meaning in the preterit. Querer and saber both fall into this category. No querer becomes "to refuse" (instead of "to not want") and saber becomes "to find out" (rather than "to know"). Use the imperfect in order to express the original meaning of the word.
Querer:
There is a large difference between "did not want" and refuse. You can still go through with something even though you did not want to do it. It is only a state of mind. To refuse on the other hand is a concrete action where you have chosen not to do something.
Saber:
The sentence does not tell of a specific time in which Juan found out about Maria coming and therefore you should use the imperfect since it is an unspecified time in the past. Mental states (knowing information) do not often have a definite beginning or end so I have normally seen saber in the imperfect rather than the preterit.
Venir:
This is actually straightforward. The imperfect tense can be translated into English as "was, were ____ something". This is similar to "estaba____" which is why some sentences can be constructed with either the imperfect or the past (imperfect) progressive.
'Not wanting to buy something' is more like an emotion than an act. 'Not wanting' is not the same as 'refusing' in that, despite not wanting to, it's possible that he still ended up buying the house (like after persistent manipulating by the salesman). The refusing was the acting on this emotion and happened at a specific time, which is why that sentence is written in the preterita.
I'm not sure about the 2nd, so I'll leave that to someone more skilled.
