Translation:My mother swims more than my father.
Just imagine that the phrase is an abbreviated form of 'My mother swims more than my father does'. Then, father is the subject of the second phrase, and thus its case is nominative. (This argument is valid for the German version as well)
Note that some very nitpicking grammarians would consider 'Older than me' instead of 'older than I' to be a mistake in (at least British) English. I don't agree with them but it may help you understand why the use of the nominative is actually quite natural here.
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.
Yes. But not in Mary Louise Thomas' classroom and not at my father's dinner table.
Nor in writing. But certainly often (exclusively?) used in speech.
But language changes and evolves. Amongst the educated in the deep south, the change is, however, not quite so quick.
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".
Sure. I'm not a native speaker and don't have a strong opinion on which one to use. Depending on your social environment, your mileage may vary. But I think it's good to view it as a matter of style, not of right/wrong.
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)"
Frequency, I think. "More" as in "more often". Perhaps length of time/duration. If this concerned physical distance, I think the German would be "Meine Mutter schwimmt ferner [oder weiter] als mein Vater."