Use Of Verb Desu
Like the English verb to be, desu (deh-soo) expresses the identity or state of people and things. Desu is used in a construction, X wa Y desu (X wah Y deh-soo; X is Y). Instead of saying "X is Y," the Japanese say "X Y is." The particle wa (wah) is the topic particle discussed earlier in this chapter.
Desu follows either a noun or an adjective. For example, Ototo wa gakuse desu (oh-tohh-toh wah gah-koo-sehh deh-soo) means "My little brother is a student." Watashi wa genki desu (wah-tah-shee wah gehn-kee deh-soo) means "I am fine." Now you know why many Japanese sentences end in desu.
Conjugation-wise, desu doesn't look like any other verb. The reason is that desu didn't start out as a stand-alone verb. It was the combination of the particle de, the verb aru (ah-roo; to exist), and the polite suffix -masu.
The table below shows the patterns of desu. To help you see the point, I use the same noun gakuse (gah-koo-sehh; student) in each example.
Formal Form of Noun Plus Desu
|gakusei desu||gah-koo-sehh deh-soo||is a student|
|gakusei ja arimasen||gah-koo-sehh jah ah-ree-mah-sehn||isn't a student|
|gakusei deshita||gah-koo-sehh deh-shee-tah||was a student|
|gakusei ja arimasen deshita||gah-koo-sehh jah ah-ree-mah-sehn deh-shee-tah||wasn't a student|
Informal Form of Noun Plus Desu
|gakusei da||gah-koo-sehh dah||is a student|
|gakusei janai||gah-koo-sehh jah nah-ee||isn't a student|
|gakusei datta||gah-koo-sehh daht-tah||was a student|
|gakusei ja nakatta||gah-koo-sehh jah nah-kaht-tah||wasn't a student||
Ja (jah), which you see in the negative forms in the above Tables, is the contraction of dewa (deh-wah).Most Japanese people use ja in everyday conversation, but they use dewa occasionally. Be prepared to hear either one.