Correcting Grammar: 'Can't Hardly' vs. 'Can Hardly'

It is curious that he can hardly tell the difference between one flower and another. The phrase 'can't hardly' is a common grammatical error. The correct way to express this idea is 'can hardly'. The word 'hardly' already conveys a negative meaning, so the double negative is unnecessary. Here's the corrected sentence: It is curious that he can hardly tell the difference between one flower and another.