In that case, you must look up a Korean dictionary. You cannot distinguish between causative and passive without knowing the meaning. Here are some examples. causative verb with -히- 묵히다/굳히다/굽히다/젖히다/앉히다/읽히다/밝히다 passive verb with -히- 막히다/닫히다/뽑히다/맺히다/얹히다/얽히다/밟히다 causative verb with -이- 붙이다/덮이다/보이다/기울이다/녹이다/먹이다/붙이다/끓이다 passive verb with -이- 깎이다/놓이다/꼬이다/쌓이다/떼이다

you don't... there is no hard and fast rule - at least one that I know about. you will just have to know them by experience