A yeshiva student said to one of his fellows, "The sages ask: What makes the glass of tea sweet? If I reply that it is because of the sugar, then I must ask: What is the teaspoon's purpose? The answer: to sweeten the tea, for which the proof is as follows: When you put the sugar into the tea, it does not turn sweet until you have stirred it with the teaspoon. In which case, why do we need the sugar at all?"

The second student replied, "Indeed, it is true that the tea is sweetened by the spoon. Now, why do we need the sugar? My reply is that sugar is necessary because it's only when the sugar dissolves that we know it's time to stop stirring."