Teach Us, Teacher
TA-form verb + KOTO GA ARIMASU (Lesson 20)TA-form verbs indicate action in the past or the perfective aspect. That is what we did in the past or what we have done. And if we combine TA-form verbs and KOTO GA ARIMASU, we can talk about what we have done before, that is, our experiences.
If, for example, we change UTAIMASU (to sing), to UTATTA KOTO GA ARIMASU, we are saying "I have sung (it) before," or "I have the experience of singing (it)." To turn this into the negative, we change ARIMASU to ARIMASEN. So, the negative form of UTATTA KOTO GA ARIMASU (I have sung (it) before) becomes UTATTA KOTO GA ARIMASEN (I have never sung (it) before).
You have to be careful about one thing. You cannot use this way of talking about experiences -- linking TA-form verbs and KOTO GA ARIMASU -- together with the terms that refer to a recent time, such as KINÔ (yesterday) or SENSHÛ (last week). In cases like this, you would simply use the past form of verbs.
So, suppose, for example, that you are asked, "Have you ever seen Mt. Fuji?" If you just saw it last week, you cannot say SENSHÛ MITA KOTO GA ARIMASU (I have seen it last week). You would need to use the past form of MIMASU (to see), MIMASHITA (saw), to say SENSHÛ MIMASHITA (I saw it last week).