The ad hominem family of flaws are irrelevant personal attacks to discredit an argument. Obviously, in real life, sometimes a personal attack is a valid one. Sometimes personal attributes do matter. If you have a history of robbing banks, it weakens your argument to work as a security agent at a bank, for example.

Ad hominem means “to the man” and indicates an attack made upon a person rather than merits of a person’s arguments.

You can strengthen an ad hominem argument by showing that the personal characteristic is, in fact, relevant.

Don’t vote for him to be President; he has cheated on his wife many times.

This argument can be strengthened by the statements:

  1. Numerous affairs could be a distraction from governance.
  2. Numerous affairs may make the president susceptible to blackmailing.
  3. Affairs could evidence poor character.

You can weaken an ad hominem argument by showing that the personal traits aren’t important.

Don’t hire him as your landscaper; he’s had many affairs.

This argument can be weakened by the statements:

  1. It is difficult to see how a landscaper’s personal life could have any impact on his performance.
  2. All of the landscaper’s clients are male, so the way in which he interacts with women is irrelevant.

Next LSAT: January 26

Argumentum ad Populum

This is argumentum ad populum, the belief that truth can be determined by, more or less, putting it to a vote. Democracy is a very nice thing, but it doesn’t determine the truth. Polls are good for telling you what people think, not whether those arguments are valid.

PrepTest 28 (June 1999 LSAT), S1, Q9 (p324)
PrepTest 28 (June 1999 LSAT), S1, Q19 (p327)
PrepTest 32 (October 2000 LSAT), S4, Q13 (p141)

Genetic Fallacy

This is a fallacy where you dismiss something based on where it came from.

Discoveries from Archimedes should be dismissed since he made them in a bathtub and not a proper university laboratory.

PrepTest 30 (December 1999 LSAT), S2, Q26 (p61)

Appeal to Authority

This is using the opinion or position of an authority figure, or institution of authority, as a trump card over an actual argument.

Ignore any scientific ideas from anyone who didn’t get a PhD.

PrepTest 20 (October 1996 LSAT), S4, Q20 (p75)
June 2007 LSAT, S2, Q17 The flip side of the Ad hominem argument is the appeal to author.

No True Scotsman

This is a “purity test” where you rebut an argument by saying that the offender really wasn’t a member of your group.

The ideas from that member of the club are wrong, but he isn’t really a member of our club as per our most recent declaration of values, so it doesn’t matter.

Next LSAT: January 26