Den / Det
I want to know the difference between "den" and "det"? Duolingo translates both words as "it" and they seem to be interchangeable so far.
But, since I'm pretty sure they are not interchangeable (why would you have to words for "it" with no reason), what is the difference between them?
Den is for en-words, det is for ett-words.
Det är en katt. Den är liten. / It is a cat. It is small.
Det är ett bord. Det är litet. / It is a table. It is small.
You're right, of course, but I would suggest not using the det är... construction for someone just learning the difference between the genders. It will probably only make things more confusing - they can learn that later instead. :)
Jag har en katt. Den är liten. / I have a cat. It is small.
Jag har ett bord. Det är litet. / I have a table. It is small.
I have written some more about it e.g. here: https://forum.duolingo.com/comment/26420394/Answers-to-some-common-questions-on-grammar-that-beginners-have - it's for en / ett but the same principle applies.
In short, Swedish nouns have different genders - en or ett. These are grammatical, not biological. You use den as the definite article for en-words, but det as the definite article for ett-words. Both also mean "it", depending on the gender of the noun the "it" describes.