"BUKAN" is used to negate things or people, while "TIDAK" is used to negate acting words or adjectives (qualifying words). Besides "bukan" and "tidak", negation in Indonesian can be also formed by using "TANPA" which means "without". Example: (1) Saya BUKAN Billy (I am NOT Billy); (2) Jane TIDAK cantik (Jane is NOT beautiful); (3) Penerbangan ini TANPA asap rokok (This flight is a NO smoking flight).