I asked this question several months ago, back when I understood that when talking about a person, one can say, "She is a short woman," - „Sie ist eine kleine Frau." Or, "She is a small woman," - „Sie ist eine kleine Frau." When discussing height, both short and small are translated as klein.
However, I've since learned that, in German, different adjectives are used when describing height (items that stand) versus describing length (items that lie).
A short path (a path that doesn't go very far, as used in your example), would be, „Es ist ein kurzer Weg." Whereas a path that isn't wide would be described as „ein kleiner Weg."
well explained. It corresponds exactly to the italian "corto" and "piccolo" (those who are studying italian too will be interested):
kurz = "corto" (or "breve")
klein = "piccolo" (or "stretto")
hence, "una piccola strada" (win kleiner weg) means a path that isn't wide and "una strada corta" (or "breve") is a short path.
Wondering what this sentence has to do in a COMPARATIVE lesson!?
I don't think learning just from duolingo would suffice. One should make some extra study on matters encountered here, in order to truly understand and organize the knowledge. Duolingo is the tool that helps you learn the vocabulary through repetition. It would be enormously more complex to cover it all, and don't forget it is free. Rosetta Stone is very similar to Duolingo and costs $200+. I'm happy Duolingo exists, with its flaws and little annoyances, and I know without it I would have never gotten so far with German. I study a lot extra and in the end it's just fine.
You have to first think of how you would write klein if it was an adjective in the sentence. Here we have nominative (because of the verb sein), masculine and singular = the adjective form is "kleiner". When you have comparative, you take the adjective form and add "er" at the end so here it'd be "kleinerer".
ein kleiner Weg = a small path
ein kleinerer Weg = a smaller path
I hope I was clear and that it'll help you :)
A thought-provoking reply from Jujubees which helped my understanding, but I think it's more straightforward thus: (STEP 1) take the adjective without its endings and prepare it (add an umlaut if necessary or if it ends in "-er", "-el" or "-en" remove the "e") --- then (STEP 2) add the "er" of comparison then --- (STEP 3) add the usual inflections that adjectives take if going before the noun.
Chrissy's comment above resonated with me!
If you had a small dog you might say "mein Hund is klein" and refer to your dog as "mein kleiner Hund" ("my little dog"). In neither example is the adjective a comparative one. The "-er" ending is the usual nominative masculine singular ending after the possessive determiner for "my". So far so good. We know this from previous skills.
If you made a comparison you might say "my dog is smaller" which in German is " mein Hund ist kleiner". Here the "-er" ending is the comparative ending. No other ending is added because the adjective is not before its noun. (In the language of grammar, it's a predicate adjective.)
That's the difference between the two "kleiner".
If you put the comparative adjective "kleiner" before its noun "Hund" you would have to add the usual inflections adjectives take, so it would be "ein kleinerer Hund" or "der kleinere Hund". In the accusative you'd have e.g. "ich sehe meinen kleineren Hund".
One consonant following a stressed vowel indicates a long vowel (e.g. die Vase, der Markt, die Türen, der Weg). Two consonants following a stressed vowel indicate a short vowel (e.g. die Mutter, die Tonne, das Bett, das Wasser). Of course there always are exceptions (like "der Bus", short u) but that is the general rule. Here it is important to distinguish between "der Weg" (long vowel, 'the way') and "weg" (short vowel, 'away' or 'gone')
In German "der Weg" is either a small path, track, trail, usually not asphalted and not necessarily suitable for cars. I assume Duolingo marks it wrong to be clear about the important difference between
"die Straße" - the road/street http://upload.wikimedia.org/wikipedia/commons/0/0b/B61_G%C3%BCnser_Stra%C3%9Fe_-Unterloisdorf.JPG
"der Weg" - the path/track/trail http://geroellundsteinhagel.files.wordpress.com/2012/01/weg.jpg
An exception is when talking about directions. "The way to Munich." translates to "Der Weg nach München.". You would not use "die Straße" here unless you are talking about one specific street.