이치가 · 이치를
reason, logic, the natural order of things
Example
노력한 만큼 얻는 것이 세상의 이치예요.
You get as much as you put in; that's how the world works.
Word parts
이 reason, principle+치 reach
Literally 'reason reached' — what makes sense by principle.
Good to know
이치에 맞다 'to make sense' and 이치에 어긋나다 'to be unreasonable' are the key collocations.