There is something strange about this sentence. Shouldn't it be "that was the end, I thought."?
I'm not a professional English speaker but it is my mother tongue and I think in German you wouldn't differentiate between "is" and "was" the same way you would in English. But I could be completely off on this, it's just one of those little things that keeps coming up when I speak German and I can't really figure it out. Any help would be greatly appreciated.
The speaker is telling you what he/she was thinking at that time. She/he was thinking "This is the end!" This happened in the past so the "thought" is appropriate. In English this sentence would be written: "This is the end!", I thought. Or even better: I was thinking, "This is the end!". The quotation marks help you to see that it is a separate time from now.
Good grief. This is absolutely standard narrative writing. The quotation "This is the end" is a fly preserved in amber. It need not match the the tense of the narrative it is embedded in. I can also, quite correctly, write "tomorrow, I may well be thinking, "This is the end.""
There are certainly situations where tense mismatches occur in writing, but this isn't one.
(Strictly speaking, it is missing some quotation marks -- but we all know Duo always disregards punctuation.)
I am a native spanish speaker, it makes sense for me. Perhaps if they had includded speech marks you'd understand as well.
Take it as though there WERE speech marks and that WAS what you thought. So, in that past time, exact and precise time you were thinking that it was present. You said to yourself 'Hey dude, it IS the end'.
Also, there was another exercise in which they used the word 'before' with two infinitive verbs, and somebody asked: hey well I see that 'before' has to do with the past, but the lesson is called preterite; and the answer was 'well hey. They are also supposed to teach when not to use it'
Unless there's someone commenting 'this is a weird phrase, you don't say this that way and I know it because I am a native speaker/ lived in Germany for ten years/ I study german since I'm little, etc', try to understand its meaning itself instead of translating it to english. Basically, because... they are quite different languages.
The verb must always come in the second part of a sentence unless it's a question (first) or has a modal (helping) verb (end). I'm not entirely sure about this next part, but I think the quote is seen as the first part of the sentence, making the verb next. If "I thought" was at the beginning, it might be Ich dachte, "blah.", because Ich is the first part. I hope that helps. This is my first time explaining German.
I give up. I confuse "das ist -> that's / it's" and "das -> the / a" all the time. I mean, is it so freaking important which article to use? "It's an end!" / "That's an end!" / "It's the end" / "That's the end" — does it really give any difference, which is important enough to freak the learner out? e.g. "im Restaurant" -> "in the Restaurant", not "in Restaurant" — what the hell? Sorry for not being an English native speaker and not getting these details as just given, but maybe it should be just simplified?
Imagine = vorstellen (not introduce!) think = denken, überlegen, glauben
Ich denke, er wird vor 18:00 zu Hause sein. /// Ich glaube, ich werde mir dieses Jahr ein neues Auto kaufen. /// Willst du mit mir ins Schwimmbad gehen? - Ich werde es mir überlegen.
Ich glaube, dass es Alians gibt. /// Ich glaube, es gibt einen Gott
No, the "das" overload is even worse because of inversion (verb to the end) in the subordinate clause, so "Ich dachte, dass das das Ende ist." is the correct version of your sentence. You usually change the word-order or choice of words in order to avoid too many "dass" and "das" in a row, e.g. "Ich dachte, dass es das Ende ist." or just like the given translation.