"Only If" Confusion

FautApprendreLSAT1

Hi Guys, I am going through the LSAT trainer and came across diagramming drills using "only if" and I am having a hard time understanding the answers. I would really appreciate it if someone could help explain?

1. H will go before J if and only if H is after M.
   My thought process: this is basically two statements in one (one for "if" and the other for "only if"
   A. H will go before J if H is after M: M-H--J
   B: H will go before J only if H is after M: I get the same answer as the one above, which means my thought process in interpreting "only if" is probably off. The correct answer is J-H-M but I don't understand how. I know that "only if" statements should result in the opposite diagrams as those of "if" statements, but this is a rule I have only memorized and do not necessarily understand. Please help and thank you in advance!

seonglee0630

when there is "if and only if" you can think that like "<=>"
in other words, H will go before J <=> H is after M
H-J -> M-H & M-H -> H-J
M-H- J

in contrast, when there is only "only if"
H will go before J only if H is after M
H-J -> M-H [not M-H -> H-J]
I hope it clears the confusion. When I read the LSAT trainer, i was also confused. There are lots of lecture in 7sages, and it gave me much clear answer.

FautApprendreLSAT1

@seonglee0630 said:
when there is "if and only if" you can think that like "<=>"
in other words, H will go before J <=> H is after M
H-J -> M-H & M-H -> H-J
M-H- J

in contrast, when there is only "only if"
H will go before J only if H is after M
H-J -> M-H [not M-H -> H-J]
I hope it clears the confusion. When I read the LSAT trainer, i was also confused. There are lots of lecture in 7sages, and it gave me much clear answer.

This makes a lot of sense. I'll probably go through the CC for a review because the trainer is definitely a bit confusing regarding thus. Thank you!