"Le plus intéressant" is not merely an adjective meaning interesting but a noun meaning "the most interesting".
"plus intéressant" would be "more interesting", but by adding the definite article, "le plus intéressant" becomes a superlative form, "the most interesting". http://french.about.com/od/grammar/a/superlatives.htm
I would say "C'est très intéressant". Why? Because your use of "most" means "very". It doesn't mean "the most". So it would be an error to try to literally translate the word "most" in isolation back into French.
that is a very good answer. as i think of it saying very interesting or most interesting in everyday conversation in english is really the same....at least to me
once again thanks for taking the time to answer
thank you for the explanation... which makes good sense... however in English the article "the" would in some way require a subject... example.. this is the most interesting thing I have ever heard...in this example that Duo uses, the English translation is somehow missing something...You n6zs being a native speaker would understand what I mean....I think that is why you get translations where people try to figure out the French "le plus"
"It is the most interesting" and "It is most interesting" do not mean quite the same thing in English. If "C'est le plus intéressant" means "It is the most interesting" then, how would one say "It is most interesting" ?
I think what is being implied here is that "It is the most interesting" is not a proper English sentence whereas "It is most interesting" certainly is. The former needs a bit of a preamble or "post-amble" to be correct. For example: "It's not the most elegant horse in the race, but it is the most interesting. Or, it is the most interesting item on the menu.
Why can "C'est le plus intéressant" not mean "HE is the most interesting"? Must it be "It is the most interesting"? Please explain :)
"C'est" only refers to a person if it precedes a modified noun. "C'est un homme" ("un" modifies "homme")
I think the pronunciation of c'est is rather difficult to understand. I wish I could use a version of Duolingo without the computer voice saying things.