If the scholar feels that he must know everything about any topic, he is in trouble – and will not publish with a clear conscience.
I think that consciousness has always been the most important topic in the philosophy of mind, and one of the most important topics in cognitive science as a whole, but it had been surprisingly neglected in recent years.
One time, I was given an essay topic: to describe a perfect horse, whom the mere sight of the rider’s whip would make obedient. I depicted this perfect horse throwing his rider at the sight of the whip.
Foreign languages are another favourite topic, and as these men are bilingual they have a fair notion of what it means to speak and think in many different idioms.
Solving climate change is a complex topic, but in a single crude brush-stroke, here is the solution: the price of carbon dioxide must be such that people stop burning coal without capture.