1.
... and go; ... away (movement away from the speaker)
Attached to the te-form of a verb, いく keeps its sense of movement away from where the speaker is: 持っていく (to take something along), 歩いていく (to go on foot), 出ていく (to go out, to leave). The verb before て says how the going happens.
2.
go on ...ing; keep ...ing from now on
With verbs of change or continuing activity, 〜ていく describes a process that continues from the present onward: 寒くなっていく (it will keep getting colder), 続けていく (to keep on doing). Its mirror image is 〜てくる, which brings a change up to the present.
Formed from the te-form of a verb plus いく. The helper conjugates like 行く: 〜ていきます, 〜ていった, 〜ていかない.
Usage
- Sense 1 pairs with 〜てくる: 持っていく (take) vs. 持ってくる (bring); 連れていく (take someone along) vs. 連れてくる (bring someone along).
- Sense 2 looks forward from now: 変わっていく (will keep changing), 増えていく (will keep increasing), 生きていく (to go on living).
Watch out
- A change that has developed up to the present takes 〜てくる, not 〜ていく: 暖かくなってきた (it has gotten warmer) vs. 暖かくなっていく (it will get warmer from now on).
Writing
- Usually written in kana as a helper; the kanji form 行く is common when the movement is literal (持って行く).
Related words
- てくる: come ...ing; change up to now
- 行く: to go