When you rely on their word
If Nora is your only source for the prices, evidence that she has altered quotes before is a reason to check the originals. Her reliability affects your evidence. It does not prove that the new printer is more expensive.
Ad Hominem
Attacking a person does not show that their claim is wrong. The mistake is letting a judgment about the speaker stand in for an answer to their argument.
Imagine a colleague shows you a cheaper printer lease. Someone replies, “Don’t listen to Nora. She’s a complete mess.” You may now think less of Nora. But you still haven’t learned whether the printer costs less.
Where Does the Reply Land?
An ad hominem fallacy takes that detour: it rejects a claim because of an irrelevant criticism of the person making it. Change the reply below and follow what it actually challenges.
Nora’s proposal
“Our printer costs RM300 a month. This new lease is RM220 a month. Switching will save us RM80 a month.”
An invented office example. RM = Malaysian ringgit.
Personal Can Be Relevant
The test is relevance, not politeness. Ask: does this fact about the speaker change how well the claim is supported?
When the evidence is checkable
If you have the original quotes, assess those figures directly. Even “You’re an idiot; you left out the toner cost” contains a relevant objection. The insult adds nothing, but the missing cost matters.
Three Ways the Detour Appears
These are different ways to skip the same job: answering the reasons given.
Attack a traitCharacter
In a policy debate: “His bus proposal must be bad. He’s an arrogant person.”
Arrogance does not tell you whether the routes serve the people who need them. Check the plan.
Dismiss a motiveCircumstances
Under a product review: “She earns a commission, so her battery-life figures must be false.”
The incentive is a reason to seek independent tests. It is not proof that the figures are false.
Point to hypocrisy“You too”
At work: “You say deadlines matter, but you missed yours. So your point is wrong.”
The colleague may be inconsistent. That alone does not refute the point about deadlines. This move is often called tu quoque, Latin for “you too.”
Bring the Reply Back to the Claim
You do not need a Latin label to redirect the conversation. Name the claim, then ask for the relevant objection:
“That may be true about Nora. Which part of the cost comparison is wrong?”
If reliability is the real concern, ask to verify the original quotes. If someone insults you, you can set a boundary and return to the evidence.
Spotting the fallacy does not prove the original claim true. It tells you that this particular reply has not refuted it.
Where the Name Came From
A debater could take a rule their opponent had accepted and show what else that rule committed them to accepting. The reply was directed at that particular person’s own commitments. That is the older use John Locke described in his Essay Concerning Human Understanding (1690), rather than the modern idea of dismissing someone with an insult.
Ad hominem means “to the person.” Locke noted that the name was already in use; he did not invent it. Later discussions developed the familiar character, circumstance, and hypocrisy categories. Today the phrase often names the irrelevant personal attack explained here, though philosophers also discuss reasonable arguments about a person’s credibility.
Judge the Claim by the Reasons That Support It.
A person can be unpleasant and right, or likable and wrong. Follow the evidence back to the claim.