Translation:My mother swims more than my father.
I don't consider myself particularly "nit-picky", but every one of my (American) English teachers (1972-1984) drilled into me "Would you say 'He runs faster than me does' or 'He runs faster than I do'?".
The first (corresponding to Akkusativ) option is wrong. The second (corresponding to Nominativ) is correct.
I see two primary benefits:
(1) Using one case or the other makes the sentence unambiguous in more complex situations, e.g., "I like my dog more than [he/him]"
(2) Recognizing which to use in English aids NE speakers in learning which to use auf Deutsch.
Since there's really no authority for "standard" English--just a sort of democratic, situational consensus--I'll concede that it is more a matter of "style" than "correctness".
No. In a comparison (positive or comparative), the things being compared have to be in the same case. Since you're comparing to the subject ("meine Mutter"), you have to use the nominative. Examples:
- "Er (nom.) ist so groß wie ich (nom.)"
- "Er (nom.) ist viel größer als ich (nom.)"
- "Ich sehe meine Mutter (acc) öfter als meinen Vater (acc)"