Possible? Yes.
Practical? No.
In order to get polyphase power, you need to store energy from the single phase source and then release it 'delayed' appropriately. You could certainly do this with a capacitor setup, but the capacitance would need to change as the load changes, and with any sort of resistive load you wouldn't be able to get a full 90 degree phase shift.
Once you had your two phases, a suitable transformer arrangement could generate any number of phases.
You will get better results with the rotary phase converter, where the energy gets stored in the inertia of the rotor, and the phase angles are set by the physical positions of the converter coils.
Two phase three wire has two phase legs and a single common conductor. Two phase four wire has _four_ phase legs, arranged in pairs.
Remember that voltage is _always_ measured between two points, eg two wires. A single point does not have voltage except by reference to another point. In AC circuits, the voltage between these two points is always changing, and you can graph voltage versus time. With a single pair of wires, you don't have phase defined. But when you have more than a single pair of wires you can graph voltage versus time for both pairs, and then describe the 'phase angle' between the two graphs.
With two phase three wire, you have supply leg A and supply leg B, and the common. If you measure the voltage A to common, and graph it, and then measure B to common, and graph that, you will see a 90 degree phase difference. This is similar to three phase four wire 'wye' service, where you have supply legs A, B, and C, and a common, all with a 120 degree phase difference.
With two phase four wire, you have legs A and A', B and B'. You measure A to A' and then measure B to B', and again find a 90 degree phase difference.
-Jon
