I know it's wrong but I don't know why :(
Hi friends 
I wish everyone is having a great time!
Here I have two sentences, I know for sure that the first one is wrong, and the second one is correct. I just don't know the explanation for I have not studied Spanish grammar that much.
English version; The same would be if you were the only boy and had only sisters.
1- Igual será si fuiste el único chico y solo tenías hermanas.
2- Igual sería si fueses el único chico y solo tuvieras hermanas.
I would really appreciate it if you can provide me with an explanation of why is it what it is in the three cases above, with an emphasis on fueses vs. fuiste!!
I don't know the rational explanation of why we follow some verbs with -ase, or -ese.
Thank you very much!
2 Answers
Those verbs ending in -ase, -ese, are in the subjunctive mood. The subjunctive is used when you want to express uncertainty, doubt, wishes, hypothetical things. There's a list of "triggers" you can study. Phrases like: ojalá... dudo que... es posible/imposible que... más vale que... etc, are followed by the subjunctive.
If you were a boy - but you aren't, this is a hypothetical thing and thus you need to use the subjunctive.
To further expound on the answer by diamante, I will make two points.
First the -se group of conjugations are an option for imperfect subjunctive, in some sense equivalent to the -ra endings. I say some sense as there are a few not technically subjunctive places you can use the -ra endings where you cannot use the -se endings. But to my knowledge anywhere you use -se you can use -ra, so I do not spontaneously use them, and substitute ra mentally when I see them. See the bottom of this lesson:
http://www.spanishdict.com/guide/spanish-imperfect-subjunctive
Here is a lesson on if sentneces on why you use imperfect subjunctive here (see my comment at the end): other lessons on imprefect subjunctive for othe situations could be reviewed if you need more.
http://users.ipfw.edu/jehle/courses/condic.htm
Real vs. unreal conditions A. A real condition is one which may actually come about or at least is viewed as a possibility; thus, in Spanish, the indicative is normally used both in the “if”clause and in the main part of the sentence: Si ella viene mañana, iremos al cine. If she comes tomorrow [she may actually come], we will go to the movies. Si nieva mucho, podré esquiar. If it snows a lot [it may really snow], I can ski.
B. Note that the English versions of the above conditions suggest the indicative by the lack of hypothesis-suggesting words such as “would”, and by not using the past tense to refer to a present-time situation.
C. In contrast, an unreal or contrary-to-fact condition is one which will not come about or is viewed as being completely hypothetical. In this case, the “if” clause in normally in a past subjunctive tense, and the main verb is in a conditional tense.
- Present or future time situations. The imperfect subjunctive is used in the “if” clause, and the conditional in the main clause:
Si yo fuera rico compraría un coche. If I were rich [I am not rich] I would buy a car. ¿Qué harías si fueras presidente? What would you do if you were president? [you aren't] Si Juana estuviera aquí, ¿le dirías la verdad? If Juana were here [she isn't here], would you tell her the truth?
- Past time situations. Past perfect subjunctive in the “if” clause, conditional perfect in the main clause:
Si la hubiera visto, habría dicho algo. If I had seen her [I didn't see her] I would have said something. Si hubieras venido, te habrías divertido mucho. If you had come [you didn't come] you would have had a great time. ¿Habrías ido a la fiesta si yo la hubiera planeado? Would you have gone to the party if I had planned it? [I didn't plan it]
Note you are using "past" subjunctive for a "future" hypothetical situation. In the lesson you could exchange the -ra endings for -se Please note that although the lesson emphasizes "hypothetical" as unreal, there are plenty of times we use this same construction for things that we perfectly expect to happen:
If you were to bring me a cup of coffee, I would be most appreciative.
I think the speaker expects to get a cup of coffee. Despite the hypothetical nature of the statement.
In English we could say: If you brought me... But that is not past tense, you did not already bring me a cup of coffee. So you cannot use the simple past in Spanish. We often use the same form in English as the simple past for what is the equivalent of imperfect past, and you cannot translate it into Spanish as simple past, as they do not use it for that. You must distinguish what you mean in English and translate it to the correct equivalent.
If you can convert it to were to do, translate as imperfect subjunctive.
If I went to the store tomorrow, I would buy milk..can be converted to If I were to go the store tomorrow I would buy milk. Imp sub in Spanish
When I went to the store yesterday I bought milk.. cannot be converted, it is true past. When I were to go to the store yesterday I bought milk makes no sense. So this is simple past. Preterit in Spanish.
