APPEAL TO POPULARITY, or "Ad Populum," is similar to Appeal to Belief. An Appeal to Popularity is the fallacy of thinking something is true, good or correct, because it is popular. Let's look at the difference:
Appeal to belief = Humans only use 10% of their brains. Everyone knows that.
Appeal to popularity = Our pills will help you tap into the unused 90% of your brain. Just ask the thousands of people who use them every day.
By the way, humans use 100% of their brains. The "10% of the brain" claim is an urban myth -- a false story perpetuated in modern times via advertising, email and media, and repeated so often that it's assumed to be true.
Here are more examples of appeal to popularity:
"I have thousands of letters in my office from people who approve of the war on terror, so it's obvious that we are doing the right thing."
"Four out of five people surveyed say our pizza tastes the best."
"Our school policies are excellent. Most parents like these policies."
Approval is not evidence of truth or goodness. But humans are often uncomfortable going against the majority. If you can convince a person that everyone else likes something, he or she will usually decide to like it too. Another term for this is PEER PRESSURE.
Appeal to Popularity is how fads are started. A fad is a temporary, often intense, interest in something that really has no inherent value. It becomes popular just because "everyone is doing it." Bell bottom pants. Smoking cigarettes. Beanie Babies. Webkinz. Silly Bandz. Can you think of any other fads?
