A residential 120V AC/60 Hz parallel circuit with one hot wire (usually black) and one "neutral" grounded conductor (usually white) has one "hot side" and one grounded side through which the current returns. (note: many of these residential circuits have green grounding wires, which are not related to the white grounded conductor. The green ground wires are not relevant to the question.) The question: If the AC source is alternating current direction and switching voltage polarity with every cycle, why don't the hot side and the neutral side reverse in the circuit along with the cycle? The hot side should become neutral, and the neutal side should become hot.