Polite Masu-form in Japanese

The masu-form (ます形) is the standard polite form of verbs in Japanese, used in formal or semi-formal speech (Teineigo). To change a dictionary verb into the masu-form: 1) Group 1 (U-verbs): change the final "-u" sound to the corresponding "-i" sound and add "-masu" (e.g., iku -> iki + masu = ikimasu); 2) Group 2 (Ru-verbs): drop the final "-ru" and add "-masu" (e.g., taberu -> tabemasu); 3) Group 3 (Irregular): suru -> shimasu, kuru -> kimasu. The negative form is "-masen", and the past form is "-mashita".