I think it's best to treat the mass noun Obst as meaning the mass noun "fruit" -- and would say that the plural count noun "fruits" corresponds best to the plural count noun Früchte.
For example, you can't eat drei Obst. If you're thinking about "fruits" as in individual, whole items of fruit, rather than as an unspecified quantity of plant-derived material (whether whole items or partial items), that's Früchte.
"The boy is eating a fruit" Why is this wrong?
Because that's not what the German sentence says.
Obst is "fruit" in the uncountable sense.
For example, if you have eaten half a banana and a scoop of watermelon, you have Obst gegessen (eaten fruit), but you have not "eaten a fruit". You have not consumed one entire fruit.
a fruit (countable) = eine Frucht
(some) fruit (uncountable) = Obst
Similarly, if you have eaten two whole pears and five whole strawberries, you have "eaten fruit" (Obst gegessen) or "eaten five fruits" (fünf Früchte gegessen).
That's not good English - the -es is on "does" and so "eat" should be in its base form, without -s.
If you really mean "Does the boy eat fruits?", that would be "Isst der Junge Früchte?" in German.
But a more common English sentence would be "Does the boy eat fruit?", which is "Isst der Junge Obst?" in German.
"Fruit" is usually treated as a mass noun in English, and in German, the mass noun "Obst" is more common than the count noun "Frucht" when not talking about one specific fruit.
Im noticing this more and more but what is up with the capitolization here? Is there a different rulenfor capitolization in German? Are capitols just treated as additional characters to be used in spellings? Are somenwords simply important in somenway that demands they be capitolized? I dontnwant to end up mispelling words because I dont know.
How do I know if I noun is a mass noun? Gemüse is a mass noun. So, it is grammatically singular. But on www.dict.cc, Gemüse has a plural form: das Gemüse, die Gemüse. Can I still consider it a mass noun as it is written here: https://www.duolingo.com/skill/de/Food/tips-and-notes?
What about Futter and Obst? Are they also mass nouns? Using the same way of thinking, Futter is not a mass noun either (on www.dict.cc it has plural a form). But Obst is a mass noun (it does not have a plural on www.dict.cc). Is it wrong the way I determine if a noun is a mass noun, i.e. if the noun has a singular form and not a plural form, then it is a mass noun; otherwise, it is not?
Gemüse is like “food”: it can be a mass noun or a count noun, but 99% of the time, it’s a mass noun. (We might read an article about “five health foods” but will tell our child to “eat your food”.)
Futter and Obst are only mass nouns, as far as I know.
Is it wrong the way I determine if a noun is a mass noun, i.e. if the noun has a singular form and not a plural form, then it is a mass noun; otherwise, it is not?
Yes, it’s wrong, or at least misleading, since some nouns can be used both as mass nouns and as count nouns, sometimes with different nuances and often with different frequencies.
Obst means a lot of fruits ?
No, not necessarily. "fruit" (uncountable) is not the same thing as "fruits" (countable)
If you eat three apples and two bananas, you have eaten "five fruits" -- five individual, whole pieces of fruit.
If you've eaten a pound of pineapple slices, you have eaten "fruit" -- but you can't say that you have eaten "fruits": did you eat one entire pineapple? Two entire pineapples? Most likely, pieces from lots of pineapples but no complete pineapple all at once.
The distinction between Obst (fruit, in general) and Früchte (individual, entire fruits) is similar in German.
It should also accept "fruits"
No, it shouldn't.
The German sentence does not say that he is eating several whole fruits (Früchte) but only that he is eating fruit (Obst).
It might be half a banana, for example. Or fruit salad made up of lots of chopped-up fruits so that it's impossible to say whether or not he has eaten a whole fruit, let alone several whole fruits.
No, that's not how German works. We don't put together verbs like that.
isst is "eats" or "is eating" for "he, she, it", or "eat" / "are eating" for "you" (one person, informal).
esst is "eat" or "are eating" for "you" (several people, informal).
isst has nothing to do with ist and is certainly not a combination of ist + esst.