Difference between -ていく and -てくる?

Question

Can someone explain the differences between v-ていく and v-てくる for me. I know that they both express some kind of ongoing action (like a place getting crowded). For example, what's the difference between 込んでいく and 込んでくる, or is it even possible to use both of these. Also, do you generally use kanji to write these? Most of the examples I can think of use v-てくる, like 雨がやんできた, or 空が明るくなってきた. How does the meaning change if I use いく instead? **Edit:** changed て行く／て来る to the more proper ていく／てくる.

Answer 1

「 水がスカートに染み込んでくる。」(Water soaks into the skirt.) and 「水がスカートに染み込んでいく。」(Water soaks into the skirt.) . They are both same meaning. Originally,「 くる。」means “come” and 「 いく。」means “go”. Some people use 「 くる。」like 「 染み込んでくる。」and some people use 「染み込んでいく。」. Using 「 染み込んでくる。」or 「染み込んでいく。」are depending on the person and both are same meanings.

I put more examples:

「空が晴れてくる。」「空が晴れていく。」"The sky is clear."

「朝が明けてくる。」「朝が明けていく。」"Morning is dawning."

「水が流れてくる。」「水が流れていく。」"Water is flowing."

「足がぬれてくる。」「足がぬれていく。」"My feet are getting wet."

About writing in Kinji for xxxくる and xxxいく, we usually use Hiragana.

Answer 2

Hiragana is more appropriate of showing how the action is progressing (It will get crowded/It's gotten crowded). If you're talking about going by train (or whatever), I think kanji are better.

TE+KURU is generally for actions that have proceeded up until this point:

雨がやんできた - The rain stopped (it has come to an end)

空が明るくなってきた - The sky became light (things progressed until it got this bright)

Generally things that have progressed to this place/time.

TE+IKU is for actions that will progress from this point:

雨がやんでいく - The rain will come to an end (at some point the rain let up and the storm is going to eventually blow out and remain clear)

空が明るくなっていく - The sky will keep getting brighter (the night sky seems lighter and it will progress until daybreak and stay bright)

Generally things that will progress or move further in space/time.

These patterns can also be used to mean "do an action while going after doing X"

ソーダを買って行った。 I bought some sodas (on my way)

コピーしてくる。 I'll make some copies (and come back)