Okay, so I automatically entered claro too, and I agree with you when it comes to how these are phrases that are used interchangeably in general use...BUT I think el mochuelo desagradable has a point here.
Lately I am paying closer attention to why things are considered "wrong" on this site and I am referring to el Diccionario de la lengua española a lot this time around because it often explains why Duolingo deviates from common usage when that is not immediately obvious.
From there I find that the difference between por supuesto (meaning "of course") and claro (meaning "clearly") and how they are applied is significant enough to trigger the error message. From duolingo's perspective, rejecting what appears to be a common synonym makes sense because there are places where the meanings do not overlap. Where is gets confusing is where your friends say "Sí, claro, por supuesto" and it is understood as three re-enforcing statements of the same ("Yeah, sure, of course").
So yes, you are right when it comes to contextual usage on the streets; but these are different ideas.
I realize after re-reading my earlier comment that I didn't make myself clear (--see what I did there??). The reason ¡Claro! is not acceptable is because it doesn't mean "Of course!" out of context, it means "Clearly!". That this is a decontextualized exclamation is exactly what inflects the meaning.
If you pointed at something and said ¡Por supuesto! observers would interpret that as you having a realization (Of course!).
If you pointed at something and said ¡Claro! observers would interpret that as you dismissing it (Well yeah... duh!).
You can argue that ¡Claro! is an abbreviated ¡Claro que sí! here, but for that abbreviation to work, you require context. This doesn't work on its own as an affirmation.
Where they overlap is in informal speech when there is a context, like when you are responding to a question from your duolingo friends (^_^).
¿Disfrutó de mi explicación?
Do you know what this means? This means that we disagree on how to interpret those two exclamations (and that they are exclamations is something I think you are ignoring). Sadly this means that I will have to live the rest of my life burdened by the fact that I think someone exclaiming "Claro!" means something other than someone exclaiming "Por Supuesto!" while you don't. This also means that you didn't read any of the earlier comments since I did mention where the two overlap, but then you wouldn't have had a reason to reflexively object, and that would be too bad.
Yet what matters is that these two words don't mean the same thing, not that I described them to your exact approval. If you can find me examples of where you think they mean the same, then I will be willing to discuss your objection.
I was taught in school that "claro que si" meant "of course", so "claro" should be acceptable.
But of course it isn't.
Even though I've learned that Duolingo doesn't speak Spanish the same way I do, "claro" should still be acceptable.
No, it's the other way around. Duolingo wasn't taught by humans. (Well, it was, but not by certified teachers, I should think.)
I'm confused by the fact of HAVING to actually use the preemptive "por" when "supuesto" alone translates out to "of course" all by itself... Can anyone help explain that pls?... I mean I get what "por" can be used for for/of/etc... but if supuesto alone means of course then why is it necessary? thx!
I'd heard this expression "¡Como no!" from a Spanish-speaking character in a movie once. When someone asked, "Can I have some soup?", the other character said, "¡Como no!" and went on to get some soup for the person who asked for it. I assumed it's an idiomatic expression to mean, "Why not!" as in "Of course!" So now I'm also curious if this expression indeed means "Of course!". Can any native Spanish clarify, please? Thanks!
I understand that the absence of an accent on the cómo (from my older post) changes the intended meaning of the word that's why I felt compelled to apologize. I'm currently using the Duo app and I don't have an option to edit my post., so sorry if someone got bothered enough to vote my second post down. :s