A multitude of questions about "sollen"
Every translation I find for the use of "sollen" seems to indicate that in present tense "ich soll" means "I should" or "I am supposed to" or "I shall". (here's a link http://german.about.com/library/blmodalv02.htm)
Regardless of the choice of English word to represent "soll", the suggestion is that in the present tense, "soll" is pretty much a commandment stating that something must be obeyed.
For "ich soltte", which is supposedly in the past in German, I find the majority of translations state that it should be "I should have". That is to say "I should have asked" would be "Ich soltte fragen". Another example, taken straight from the Dartmouth website: "Sie sollte die Bücher mitbringen." = "She was supposed to bring the books along." Granted, if you translate "I should have" to German, you can also get "Ich habe gesollt", but let's skip over that for now until I get this issue better under control... I have read other suggestions that this form of "should" (the past tense) just implies that it is mearly a suggestion and not an "order" like the present tense version of "sollen". So "Ich soll fragen" would (according to this explanation) be "I should (must, absolutely have to) ask", and "Ich sollte fragen" would be "I should ask" (almost as though you have a doubt and you say to yourself "well....I probably should ask as it might be the polite thing to do"). Other than context, there is no difference between the two written sentences (in English), and the second one is most definitely not in the past tense. If it was in the past tense, as all my dictionaries suggest it should be, it would read "I should have asked". As in, "I know that I was wrong to take the car last night. I should have asked you first."
I've read, and re-read random bits of info from websites (some contradict each other), I've read through the posts on Duolingo (including a long one about "sollen" between wataya and siebolt, both of which I follow extensively as they seem to know what they're talking about in German) but I have yet to see any reasoning or explanation for Duolingo's use of the present or the "past" conjugation of "sollen". And, if "ich sollte" really is in the past, and really does translate to "I should have", then what is the reasoning behind it always being marked wrong? It can't simply be a programming error, so is there a whole other set of rules that I can't seem to find, where "ich sollte" it is in the past, but not on these specific special occassions? Thanks for listening, and thanks in advance to anyone that can offer me some clarity on the matter.
The pons entry for 'sollen' is rather informative as it provides a lot of examples: http://is.gd/eaPNoo Unfortunately, 'sollen' is one of those words that has so many different uses that it's impossible to discuss it in its entirety. Menschenkind already mentioned that 'sollte' can be past tense or Konjunktiv II.
Wait a minute what. Now, that's a whole lot. Let me try to start small and we'll work our way through, okay? What you are missing, in my opinion, is the subjunctive. 'Ich sollte' in a present tense is a subjunctive form.
Ich soll gehen = I'm supposed to leave.
Ich sollte gehen = I should actually leave, but I'm either too lazy or just enjoy it a lot here. (subjunctive)
Ich sollte gehen = I was supposed to leave.
Ich hätte gehen sollen = I should actually have left, but... (subjunctive)
Ich habe gehen sollen = I have been supposed to leave
The subjunctive switches the verb one tense backwards, to the past. Maybe I'm missing something. Feel free to correct me and excuse me if I got the tenses wrong in english.
Okay, so what I'm getting from you, and from looking at wataya's link, is that I first have to study subjunctive in English and get a grasp on that before I even try to understand the German version. I'm pretty sure that is the part I'm missing because every time I saw "sollte" I was under the impression it was supposed to be in the past tense.
Thanks to both of you for the replies! I'm going to have to go read a bit before I can go any further.