depend on/upon

1 :  to be determined or decided by (something) We're not sure if we'll have the picnic. It depend s on the weather. “Will you go back to college?” “I don't know. It depends on whether or not I can afford it.” The stamp's value depends on how rare it is. Depending upon your child's weight and height, she or he may have to sit in the back seat of the car.

2 :  to need (someone or something) for support, help, etc. He no longer depends on his parents for money. They depend heavily/largely/solely/entirely on her income to pay the bills.

3 :  to be sure about (someone or something) :  to trust (someone or something) The manufacturer promises quality you can depend on. She will be remembered as a woman upon whom people could depend. —sometimes used humorously I can always depend on it to rain on days when I forget my umbrella.