More on Progressive Form

There's another use for the progressive form in Japanese, although it may be better to call it the ている form to avoid confusion. In English, we simply use the present tense to declare certain states. "I have lots of money" or "I know your sister" are two examples. However, in Japanese, the ている form would be used in both of those cases. I'll try my best to explain the reasoning.

If I have lots of money, that is sort of like a continued state. It doesn't refer to a state that's only true at this exact moment. The same is true with "I know your sister." I don't cease to know her after the sentence is finished. My knowledge of her is an ongoing state that continues to be true. So, rather than use the present tense to say that I know her, I would use the ている form because I want to convey that I'm in a state of knowing her.

Because this is an entirely new concept and is a bit difficult to comprehend at first, I'm going to copy some examples directly from my Genki textbook. The following are common verbs that use the ている form to convey a continued state.

結婚している - is married

座っている - is seated

持っている - has

知っている - knows

太っている - is overweight

やせている - is thin

着ている - wears/is wearing

起きている - is awake

住んでいる - lives

勤めている - works for

The verbs 行っている and 来ている are very common, as well. In this form, they do NOT say "is going" or "is coming." What they do is "indicate the current state that resulted from prior movements" (from Genki).

アヤトはカナダに行っている。
Ayato has gone to/is in Canada.

ライトは家に来ている。
Laito has come over.

This is probably the most difficult concept I've studied to date because, like I said, it's rather different from English. But at the same time, it almost makes sense intuitively. I think I would find it strange to read 姉を知る (I know your sister, plain present tense) because it just sounds wrong. With ている we are describing a continued state in which we know her, and that makes sense.