YOU SAID:

If something goes up then it must come down

INTO JAPANESE

何かが上がるなら、それは降りなければなりません

BACK INTO ENGLISH

If something goes up, it has to go down

INTO JAPANESE

何かが上がるなら、それは下がる必要があります

BACK INTO ENGLISH

If something goes up, it needs to go down

INTO JAPANESE

何かが上がったら、下がる必要があります

BACK INTO ENGLISH

If something goes up, it needs to go down