tell the difference, discriminate

(くべつ) To tell the difference between two similar things. If you want to tell your Japanese friend, “I can never tell the difference between the synonyms X and Y,” then you’d use 区別出来ない!   TTT
(さべつ) In theory this means the same as 区別、 but in practice it’s almost always used to mean ‘discriminate’ – as in bigotry. The only exception is the phrase 差別化、 which is corporate-speak for “make our products stand out from the competition.”   PPP