"He eats nothing but fruit."
Translation:Er isst nichts außer Obst.
As far as my understanding, außer is similar to "besides" or "excluding". It's also used as "but," however the word "but" has many meanings.
Meanings of BUT:
But1: However; denying or going against the previous fact
But2: Exclusion. E.g. I will meet anyone but her.
But3: Impossibility. E.g. I can't help but falling in love. (= it is impossible not to fall in love). Nothing I can do but observe (= It is not possible for me to anything; only can I observe.)
aber is the first definition of But
außer is the second definition of But.
als is not but, rather it means "than"
Now, als means "than" in English. I don't know if "Er isst nichts als Obst" is a natural sentence, because I'm not a native, but in this case the sentences would translate to "He eats nothing other than fruit".
This is incredibly useful, thank you ever so much. Does "sondern" fall into the denying element, by any chance? As in: "It is not raining, it's rather sunny." or "He is not my brother, but/rather my friend." I've seen it used plenty in this context to correct a formerly denied statement or clarify a situation, and it's making me nitpick the word.
"Sondern" is used as a conjuction; it translates "but" when it has a meaning similar to instead, rather. E.g.:
"I don't like cats, but (rather) dogs." — "ich mag nicht Katzen, sondern Hunde."
"I didn't write you this letter, but (rather) that one over there." — "ich habe dir nicht diesen Brief geschrieben, sondern den da drüben."
"You shouldn't ask me, but him (instead)." — "Du solltest nicht mich fragen, sondern ihn."
"Außer", on the other hand, is a preposition meaning except; it translates "but" when it means excluding, except. E.g.:
"I don't like any dogs but/except mine." — "Ich mag keine Hunde außer meinem."
"Everyone but me was invited." — "Jeder außer mir wurde eingeladen."
"Außer" can also be used as a conjuction with the meaning except (for).
- "I always like you, except when you are mad at me" — "Ich mag dich immer, außer wenn du mir böse bist."
"Aber" can be used in all other cases:
"I like cats, but not dogs." — "Ich mag Katzen, aber ich mag keinen Hund."
"I love him, but he doesn't love me." — "Ich liebe ihn, aber er liebt mich nicht."
"Doch" is very similar to "aber" and has no semantic difference, but is slightly different in usage. One collocation I have observed, for example, is with zwar:
- "The noise is certainly annoying/it is true that the noise is annoying, but it is necessary." — "Der Lärm stört zwar, doch er ist notwendig."
Details for the use of ß and ss can be found here: http://german.about.com/library/weekly/aa092898.htm
Rule of thumb: if you cannot remember the correct spelling use the ss and pretend you are Swiss :)
In short, ß was changed to ss when after a short vowel, but kept after a long vowel or a diphthong (au, äu, ei, eu, ai), which incidentally makes it easier for a learner to remember certain pronunciations.
For example: "Fluss" has a short u (pronounced similar the oo in "foot" or "book") so you spell it with ss, but "Fuß" has a long u (pronounced similar to the oo in "food" or "brood") so you spell it with ß; "außer" has a diphthong (which phonologically has the same length as a long vowel) so you also spell it with ß.
When writing in all capitals, however, SS is the advised form for all cases, even though some designs for a capital eszett to be used in these circumstances have been made (ẞ as opposed to ß). So the standard all-caps for "Fuß" is "FUSS" but you could write "FUẞ".
In Switzerland, instead, it is always ss.
It is not poorly explained by Duo but they use the wrong example. Nichts means nothing and nicht means not. In English, you don't use an article after "but" when you mean it like it is meant above. So, the sentence says: He eats nothing but fruit. You don't say: he eats nothing but the fruit. In German they don't say: Er isst nichts ausser dem Obst, they just say "Obst", like the English say Fruit. Do I make any sense at all for you?
Because that's a different “but”. “Aber” represents the adversative conjunction “but”, as in “I like pizza, but I don't like mozzarella”; “außer” is instead the translation for the preposition “but”, as in “I hate everyone but you”. Basically, if you can substitute “except” for “but” in a sentence, then use “außer” in German.
There's actually also a third meaning of “but” that is also a conjunction and translates into “sondern” and that is the ”rather-but”. The best rule of thumb is: if you can say “but rather” instead of just “but”, then use “sondern”; but the best thing to do is to learn the type of sentence in which “sondern” is used, like: “he's not eating apples, but oranges“ = “er isst nicht Äpfel, sondern Orangen”.
Aside from the obvious but very important grammatical difference (‘Obst’ is a singular collective noun, while ‘Früchte’ is the plural of the count noun ‘Frucht’), the main difference is that ‘Obst’ is mostly a culinary term, while ‘Frucht’ is mostly a biological term; inedible fruits are still Früchte but not Obst and tomatoes could technically be argued to be Früchte but they are definitely Gemüse, not Obst. The different grammar also makes a difference: if you want to refer to a single item you're going to use ‘Frucht’, because ‘Obst’ would always refer to fruits as a whole. Furthermore, ‘Frucht’ can be used figuratively (as in ‘the fruits of one's labour’, ‘die Früchte seiner Arbeit’), while ‘Obst’ cannot. Other than that, the choice depends on certain set expressions and personal preference.