"The pencil is a thing."
Pretty sure 이 is used, when there is a 3rd letter in the previous sign (방이) and 는 is used when there is none (이는). I hope that's right
From what I understand 이/가 and 은/는 are more or less interchangeable, though 이/가 puts more emphasis on the subject.
And you use 이 when the previous word ends in a consonant, and 가 if it's a vowel. Same between 은/는. Like a/an 2in English (though different meanings)
Are you sure Duolingo? It might be an illusion cast down from a higher dimension into our realm. For all we know it could be a shadow of a 4th dimensional pencil...
I heard that when you have a syllable finished in ㅂ and the following one starts with ㄴ (and maybe ㅁ, but im not sure about the last one) you either don't pronounce the ㅂ or pronounce as ㅁ
Why is the article on the noun 이 instead of 은? The tips and notes page for this lesson says 이/가 is to mark who/what is performing an action, whereas 은/는 is to mark who/what the speaker is talking about. Since there's no action here, shouldn't it be 연필은?
Yeonpili mulgeon ibnida. Though I don't think translating that way from any language will help you learn it. You must understand the language and turn it into yours.
I said 연필 물건입니다, and Duo said I have a typo (first word should be 연필이), are markers that optional?