Explanation

The bandwagon fallacy is committed by arguments that appeal to the growing popularity of an idea as a reason for accepting it as true. They take the mere fact that an idea suddenly attracting adherents as a reason for us to join in with the trend and become adherents of the idea ourselves.

This is a fallacy because there are many other features of ideas than truth that can lead to a rapid increase in popularity. Peer pressure, tangible benefits, or even mass stupidity could lead to a false idea being adopted by lots of people. A rise in the popularity of an idea, then, is no guarantee of its truth.

The bandwagon fallacy is closely related to the appeal to popularity; the difference between the two is that the bandwagon fallacy places an emphasis on current fads and trends, on the growing support for an idea, whereas the appeal to popularity does not.

Example

(1) Increasingly, people are coming to believe that Eastern religions help us to get in touch with our true inner being.
Therefore:
(2) Eastern religions help us to get in touch with our true inner being.

This argument commits the bandwagon fallacy because it appeals to the mere fact that an idea is fashionable as evidence that the idea is true. Mere trends in thought are not reliable guides to truth, though; the fact that Eastern religions are becoming more fashionable does not imply that they are true.