What is the difference between ad populum fallacy and appeal to authority fallacy?

Ad populum (or appeal to popularity) fallacy and appeal to authority fallacy are similar in that they both conflate the validity of a belief with its popular acceptance among a specific group. However there is a key difference between the two:

  • An ad populum fallacy tries to persuade others by claiming that something is true or right because a lot of people think so.
  • An appeal to authority fallacy tries to persuade by claiming a group of experts believe something is true or right, therefore it must be so.