I have the same question here as Jon345104. In a later question in this lesson I had the sentence Θέλω να έχω τηλεόραση, which is marked correct. I don't see any difference between that sentence and this sentence, unless this sentence is saying that 'my son only wants one bed', in which case the English phrase should be clearer about the meaning of this phrase.
I have posted this on another question (https://forum.duolingo.com/comment/24735591?from_email=comment&comment_id=37080817), and I have tried to find some rules/research on this, but it honestly is confusing.
It's uncommon but not ungrammatical, so I've added it. Now, here's the thing: Someone is much more likely to say "You know what? I want a TV" (especially in case you have a son/daughter, you're more likely to hear "Muuuuum/Daaaaaad I want a TV!" than "Muuuuum/Dad I want a bed!". It's obvious that your son/daughter would want a/one TV for themselves, hence the omission of the indefinite article, because, how many TVs are you going to buy? 15? Now, about the exercise in discussion, if you think of this sentence as part of a dialogue at a hotel or something like that, it obviously makes a difference if someone wants one or two beds because they will pay a different amount of money. "Ο γιος μου θέλει κρεβάτι" (which, I repeat, has now been added) will probably make the interlocutor think that the bed at your place is in a bad state and needs to be changed. Asking for a TV is one thing, asking for a bed is another.
Thank you for explaining :). I admit this absence of the indefinite article does my head in :).
So I'm trying to create a rough rule for myself, and I know any rule will have its limitations, but at least as a guidance: - Unless we want to make it clear we absolutely expect only the one instance, we can drop the indefinite article. Would you agree with this rough rule?
Can I ask a follow up question? Are there examples where you can drop the indefinite article with an adjective plus noun? If I understand the answer on the other question I mentioned above correctly, adding an adjective would basically define the noun to a subset of what it is, so you need an article there to make it indefinite again. Basically, I'm wondering if "Θέλω να έχω ακριβή τηλεόραση" is correct? I'm thinking you would need an indefinite article here, but not sure.
Thanks again for taking the time to explain this. Haven't found any resources about this online.
In general, the rule of thumb is that you should use the indefinite article if there's room for ambiguity (quantity-wise) - that's why Greek doesn't (in 99,9% of cases) use the indefinite article in statements like "My aunt is a teacher", because, duh.
About your second question, you're right. One may hear an indefinite article here and there, but in general it's safe enough to extrapolate and say that you *shouldn't" use the indefinite article before an adjective + noun compound. Don't try to make a rule out of this - you won't find one. It's just a matter of usage.
(You can use the search bar of the web version to access many discussions of this kind.)