In PNP transistors, what must be true for the transistor to conduct?

For a PNP transistor to conduct, it is essential that the base is at a lower potential than the emitter, which indeed means that the base needs to be negative with respect to the emitter. When this condition is met, holes (the majority charge carriers in PNP transistors) move from the emitter into the base region.

In a PNP transistor, the emitter is typically connected to a positive voltage, allowing holes to flow into the base where they recombine with electrons. For the transistor to be in the "on" state or in active mode, this potential difference must be maintained. If the base is positive relative to the emitter, it would inhibit the flow of holes, preventing current from flowing through the transistor.

Hence, the correct understanding revolves around how the relative voltages influence the conduction state of the transistor, specifically focusing on the roles of holes as majority carriers moving from the emitter to the base when the base potential is appropriately low compared to the emitter.