Headlights only work when my brights are on. Do i need to replace both bulbs?

The low beams do not work. When I turn the switch all the way to the right the low beams do not turn on. When I switch the high beams then the headlights turn on. I checked all the fuses for the high beams and lows beams and they are fine. I replaced one of the bulbs to see if it made a difference and it did not. I'm not sure where to go from here