The naturalistic fallacy originates from G. E. Moore, a British philosopher, in his book Principia Ethica (1903); it is an appeal to (or having an inherent bias for) nature saying that what is natural is right or good and that anything unnatural (for example, synthetic or human-made) is wrong or bad. For example, advocating that vaccines are unnecessary on the basis that the human immune system can conquer disease naturally (without medical assistance) fails to regard the fact that vaccines have saved innumerable lives from diseases like polio.

Avoiding these logical fallacies goes a long way toward building ethos with your audience—particularly if the audience is hostile toward your speech topic. You want to rely on facts, research, honest emotion, and your own well-rehearsed presentation to persuade your audience. If you’re finding yourself slipping into any logical fallacy to persuade your listeners, you are lacking solid, compelling evidence in that area of your speech.