te form negative vs negative form (HW: やっていない, why not やらなかった　or　やっていなかった)


I've been studying Japanese here in Tokyo from scratch for a good 2 months
now. I've been struggling with daily conversation but I try to improve each
day by studying.

Lately, I am trying to understand when to use `~te form + iru/inai` vs
`masu/masen`. Don't get me wrong, this post is not about asking help for
conjugation techniques, but rather which one to use especially for
conversations. To `~te` or not to `~te`, that is the question.

For example:

When people ask if I did homework, I know the correct way of saying "I didn't
do it" would be `やっていない`. I was wondering why, or rather, what would be the
difference if I responded with `やりませんでした/やらなかった` or `やっていなかった`? Because the
way I see it, I was not able to do my homework which was given in the past
(probably like yesterday for example), therefore I should use past tense.
Also, why not plainly use やりませんでした/やらなかった. Why does it have to be in `~te
form`?

Another example I have is:

What would be the difference between `けっこんした` vs `けっこんしていた`? I know the first
one means "I got married in the past", does the second one mean "I was married
in the past.. but now I am not!" ~ kind of nuance?

I know this might be something very basic, but for someone like me, it's hard
to grasp it. Any feedback is much appreciated. Thank you!




「宿題をやらなかった。」means not only "I didn't do my homework",but also "I didn't have
the intention to do my homework".And it also means "I'm saying just the fact
that I didn't do my homework yesterday".So that words are used when you wanna
say "I didn't do my homework,but I"ll do it today".

「しゅくだいをやりませんでした。」is polite version of 「宿題をやらなかった。」.

「しゅくだいをやっていない。」means "I didn't do my homework,and I've not done my homework
yet".And this wors let the other person imagine that he possibly could not do
it for some reason.

「しゅくだいをやっていなかった。」means "I used not to do my homework(,but I do recently)"or"I
didn't do my homework (,but I finished it a little while ago)".

About 「けっこんした/けっこんしていた」,your idea is correct.




「宿題をやらなかった。」means not only "I didn't do my homework",but also "I didn't have
the intention to do my homework".And it also means "I'm saying just the fact
that I didn't do my homework yesterday".So that words are used when you wanna
say "I didn't do my homework,but I"ll do it today".

「しゅくだいをやりませんでした。」is polite version of 「宿題をやらなかった。」.

「しゅくだいをやっていない。」means "I didn't do my homework,and I've not done my homework
yet".And this wors let the other person imagine that he possibly could not do
it for some reason.

「しゅくだいをやっていなかった。」means "I used not to do my homework(,but I do recently)"or"I
didn't do my homework (,but I finished it a little while ago)".

About 「けっこんした/けっこんしていた」,your idea is correct.

