Classification of Japanese sentences

II. Four types of desu
Desu is classified into four types according to its usage.

A. Desu shows the equality of the two nouns.

Examples
1. Arisu san wa Ejiputojin desu.
"Alice san is an Egyptian."
2. Ano otoko no hito wa Ruin san desu.
"That man is Mr. Lwin."

B. Desu used with a -na adjective

Examples
1. Kyoo wa genki desu.
"Someone* is fine today."
(*"Someone" may be the speaker.)
2. Ano tatemono wa kiree ja arimasen.
"That building isn't beautiful."

C. Desu makes the polite form of an -i adjective.

Examples
1. Migi no me ga akai desu yo.
"Your right eye is red."
2. Mainichi isogashii desu.
"Someone* is busy everyday."(*"Someone" may be the speaker.)

D. Desu used as a substitute for a verb mentioned previously

Examples
1. A : Shokudoo wa doko ni arimasu ka.
"Where is the cafeteria?"
B : Koogakubu no mae desu.
"It's in front of the Faculty of Enginnerring."
2. A : Kinoo dare ni aimashita ka.
"Who did you meet yesterday?"
B : Kaarin san desu.
"I met Karin san."

As mentioned in Lesson 4, NOTES ON CONVERSATIONAL GRAMMER I, desu cannot be used alone. It follows a noun.