You do or don't.
You can or can't.
Can and don't is merely a subgroup that misses the idea of the comparison.
You could say the three types are "Can and do understand", "Can and do not understand", and "Can not and do not understand", but that is getting more specific than the ideal of the comparison calls for, which is usually an either/or comparison. It is akin to taking the comparison "There are three types of haircolours in the world: Auburn, Blonde and Brunette" and adding in those who change their colour. Now rather than 3 types, you have 9, but the added level of complexity is merely two comparisons overlapping. Natural hair colour and resulting hair colour. You could add hair length, hair style, eye colour, etc. to that and increase the number of types exponentially. |
