Postby jaboyak » June 3rd, 2009 5:44 pm
Okay, here's a way to explain it that I hope helps you out a little. Bear in mind that it's a little hard to explain to a beginnner before they just get used to it and learn where and when to use it.
One way "desu" is used is to be a polite marker, but also as "is" or "are".
Examples:
Sore wa takai.
Sore wa takai desu.
That is expensive.
Both of these are grammatically correct, but in this situation, "desu" is used as a polite marker. In the plain/everyday form, "i" adjectives can properly end a sentence, whereas if you were talking to a stranger, you should add "desu" to mark your politeness
Sore wa kantan.
Sore wa kantan desu.
That is simple.
The first one is NOT grammatically correct. The "desu" is being used here for "is". This is where it gets kind of complicated. With "na" adjectives, the plain form would add "da" at the end of the sentence, which is the plain form of "desu" when it is used for "is" or "are".
As far as "He is sitting on the couch" goes, don't worry about that yet. You will learn that conjugation of the verb later, which is the -teiru form.
Anyway, I hope that helped a little... haha.