As far as I know, both of these have a similar meaning. Are both interchangeable? In what situations would 変 be preferable over おかしい?
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1Do you include or exclude the cases where 変 is interchangeable with 連体詞「おかしな 」?– Chocolate ♦Dec 8, 2017 at 13:27
1 Answer
They are not as interchangeable as you might expect. I recommend sticking to 変 when you are going to express general "weirdness". 変 is somewhat broader to mean "inappropriately unusual", while おかしい is when the strangeness reminds of dysfunction of some sort.
この式は変だ
この式はおかしい
This formula is...
Even when you can use both, 変 here means giving impression of strangeness or counterintuitivity, but doesn't (necessarily) imply logically wrong (=dysfunctional), while おかしい does.
○ 変なことするな
× おかしいことするな
"Don't do anything I wouldn't do."
In this case, what they advice against to do probably has some bad effect, but not necessarily out of insanity (maybe they just intend to do), thus おかしい is not likely used.