A patient speaks rapidly and at length, moving quickly from one topic to the next, each new idea clearly triggered by a word or sound from the last, so that a listener can always follow exactly how she got from one thought to the next, even though she never settles on any single topic. Before revealing the answer: is this formal thought disorder?

No, this is more consistent with flight of ideas than formal thought disorder. Here, the individual connections between successive ideas remain understandable throughout — the listener can always follow exactly how one thought led to the next — even though the overall direction and topic are quickly lost amid the pace and volume of ideas. Formal thought disorder would instead involve the connections between ideas themselves becoming difficult or impossible to follow, which is not the case in this rapid but logically-linked presentation.