Expressions (phrases, clauses, etc.), I-adjective (keiyoushi)
bad; wrong; naughty
このフロッピーをフォーマットしてはいけません。You mustn't format this floppy disk. must not (do, be); should not; ought not to
after the -te form of a verb or adjective
useless; no good; bad
hopeless; beyond hope
unfortunate; a shame; a pity
used to express sympathy
unable to drink (alcohol)
so as not to ...; so that ... (won't); in case ...; for fear that ...; lest ...
as ...(すると/しては)~(から/ので)
Also written イケない