Ad Hominem
A type of informal fallacy where you attack the person making the argument instead of the argument itself. This can take the form of blatantly attacking someone in the form of name calling or more subtly attacking an individual’s character in an attempt to defame the argument instead of engaging with the argument directly.
Logical Form
Person 1 claims A.
Person 2 responds by saying that Person 1 is an imbecile, moron, has brown eyes, is privileged, [insert diatribe here], etc.
Therefore, A is not true.
Examples
The following abbreviations are used in the examples below:
PN = The Nth premise for N = 1,2,3,…. (e.g., P1 is the first premise, P2 is the second premise, etc.)
C = Conclusion
1) Henry is talking to his group of friends about how not only are vaccines especially effective at preventing disease [1], but they are also immensely safe as well according to science. Following Henry's remarks, one of his friends comments:
P1: Henry got a C on his Chemistry test last week.
C: So, he clearly doesn't understand science well and is wrong here about the science.
Explanation: While it is important to question a source's credibility, a proper response from Henry's friend would have been to address the statement regarding vaccine safety and efficacy. In other words, the C that Henry received on his Chemistry exam is not an adequate reason to dismiss Henry's claims.
2) Bill, a precocious 12 year old, is at a family party when the topic of conspiracy theories comes up. Nick, Bill's Uncle who also happens to be a distinguished MD and well respected within the family, goes on about how he believes that global warming is a hoax manufactured by politicians and clean energy business interests. Bill, politely responds by explaining the scientific consensus on global warming and how the scientific evidence from physics to geology all point to the same conclusion; that humans are undeniably warming the planet at a rate 170 times that of baseline [2].
Nick then retorts with:
P1: What could you possibly know as a 6th grade student about the science of global warming.
C: You’re wrong.
Explanation: Nick is clearly at fault here as he is using Bill’s age to dismiss his claims about the scientific consensus surrounding global warming. A proper response would have been to address the science regarding global warming and argue from there.
3) Beth is a cancer researcher at a local University studying immunotherapy and how it could potentially be used as an effective treatment for breast cancer. In her spare time, she runs a blog with accompanying social media such as Facebook, Twitter, etc.. Recently, she posted on her Facebook page about how Cannabis has not yet been shown to be an effective cancer treatment in clinical trials and that people shouldn't be promoting it as such; it is prudent to wait until it has been properly studied [3]. Unfortunately, as a result, she has drawn the ire of the “alt-med” crowd who have been bombarding her post with insults.
One recent comment stated:
P1: You're nothing but a shill for “big pharma!”
C: You have no idea what you're talking about.
Explantion: The owner of said comment is clearly attacking Beth instead of the argument. Specifically, Beth is being accused of being clandestinely paid by a pharmaceutical company to publicly obfuscate Cannabis as an effective treatment for cancer (Note, using Cannabis to treat cancer is vastly different from using Cannabis to treat the symptoms of cancer treatment). A proper comment would have linked to peer-reviewed science demonstrating Cannabis as an effective cancer therapy and that Beth was mistaken. However, currently, no such research exists as Cannabis has NOT been shown to be an effective treatment against cancer. Regardless, even if the commenter was unable to produce credible science to support his/her claims, a proper response should have addressed Beth's claims and not attacked Beth directly.
4) Two politicians were engaging in a public debate when the topic of “trickle-down economics” was presented as the next talking point. Politician A started by talking about how this type of economics has been tried for decades and never works as promised. That, in reality, it is nothing more than a cruel charade that is being used to transfer wealth away from the majority of Americans to the most wealthy.
Politician B, who was a proponent of the economic policy, retorted with:
P1: Well, you're a low IQ individual.
Politician B had nothing to add after this snarky comment.
Explanation: Politician B is committing the ad hominem fallacy here. Instead of addressing Politician A's claim about trickle-down economics, Politician B attacked the intelligence of Politician A. Note, technically Politician B didn't structure a complete argument as there was no conclusion presented just the premise “you're a low IQ individual.” However, since nothing was said after this comment, it's safe to assume that Politician B was implying that Politician A's claims regarding trickle-down economics were wrong because he/she is a “low IQ individual.”
Conclusion
As is always the case, if you find yourself confronted with this fallacy in everyday discourse, it is important to remember that it renders the argument bad and should be rejected. What is more, if you find yourself using this fallacy within one of your own arguments, as an individual who ascribes to the ethos of Critical Thinking, you must replace it with a good argument.
References
[2] Owen Gaffney and Will Steffen. The Anthropocene Review (2017). Vol 4, Issue 1, pp. 53 - 61.
[3] Cannabis and Cannabinoids. National Cancer Institute (2018).