Deductive reasoning.

A biology teacher wished to demonstrate to his students the harmful effects of alcohol on living organisms. For his experiment, he showed them a beaker with pond water in which there was a thriving civilization of worms. When he added some alcohol into the beaker the worms doubled-up and died. "Now," he said,” what do you learn from this?" An eager student gave his answer. "Well the answer is obvious," he said " if you drink alcohol, you'll never have worms."