I obviously realize that "το κρεμμύδι" is "THE onion," but the definite article is almost always omitted in English in copular sentences about general truths (e.g. "Life is hard," "Horses are fast," "Trees are plants," etc.). I know many languages do not allow the omission of the article in these cases, but in Greek I am not sure, so my question is this: Is there a difference in meaning between "Το κρεμμύδι δεν είναι φρούτο" and "Kρεμμύδι δεν είναι φρούτο"? Is the first sentence referring to a specific onion? Is the second sentence ungrammatical?
I thought so, but thank you so much for confirming. All the same though, "Onion is not a fruit" should be accepted for the translation into English because in English "The onion is not a fruit" is ungrammatical (except in a circumstance when one is referring to a specific onion, but that would be very rare since all onions are not fruits, so to make the distinction between "onion" and "the onion" in this sentence sounds weird).
Onions are not fruits is not correct. It should be Onions are not fruit. We only use the plural when more than one type of fruit is being discussed. Since there is only one item (the onion) "fruits" cannot be used here.
Onions and potatoes are not fruits would be a possible sentence.
(Too many nested comments, replying here.)
The sentences of the Incubator all seem correct to me. Only "Onion is not a fruit" which I see above, I cannot believe is correct.
The question though is (and I've noticed that in other sentence discussions too): you amend a sentence and its associated alternatives, but do the rest of us still see the original (with the mistake) in the sentence list? It may be fine when doing the lessons but the mistake is still the visible answer in the sentence discussions accessed via the forum. Which is obviously not ideal if non-contributors go through them trying to help.
I don't know exactly how the system works, but I think that if a mod/contributor change the best translation (which is the sentence that learners see), the new sentence will replace the old mistaken sentence automatically.
Some hours ago, the English sentence in this discussion was The onion is not a fruit and now it is An onion is not a fruit
"The onion is not a fruit" is grammatical in both the specific and general sense. For the later, it is a higher register idiomatic use of the definite article to refer to an entire species: e.g. "The domestic cat is a member of the genus Felis." Obviously, this is a true statement about any individual housecat, but it is primarily a statement about the biological species Felis catus, just as "The onion..." would by default in this sentence refer to the entirety of Allium cepa.
(Obviously, it needn't just be biological "species" for this structure to word: "The chair is a type of furniture" works just as well.)
I have been curious to ascertain if the Greek had this particular nuance. I gather that the answer is no.
All double consonants were pronounced as such in ancient Greek. For example ΑΛΛΑ was pronounced "HAL-LA" until late antiquity or early middle ages while today we pronounce it "ALA". So the answer to your question is that in standard modern Greek orthography reflects ancient pronunciation. It has remained unchanged since antiquity despite evolution in pronunciation the last 2400 years.