To become a more effective scientific skeptic, you need to know your logical fallacies. This is part two of my irregular series – my first was on the middle ground fallacy. Today’s focus is a very, very common fallacy: Tu quoque.

The tu quoque argument ( Latin for “you, also”) is a type of ad hominem argument – literally, “to the person”. It is a statement about the person, and not about the the statement being made. In my posts about homeopathy, this fallacy is frequently used by commenters. For example, I recently posted about an uncritical endorsement of homeopathy by a medical doctor. Notably, that physician acknowledges that homeopathy has no medicinal ingredients – it is a placebo. Not surprisingly the responses from homeopathy advocates ignores the consensus that homeopathy has no medicinal effects. Instead the comments tend to cite problems with real medicine. Commenter Avijit first quotes from a commentary in JAMA that claims:

225,000 people have died in one year in the US alone due to iatrogenic diseases. Of these 140,000 has been exclusively due to adverse drug reactions. In addition, an equal number died during out patient management of Adverse Drug Reactions that cost the buyer a total of $ 79 billion in prescription bills in one year.

Once again, the Death By Medicine gambit. He goes on to quote David Eddy, to imply that evidence-based medicine isn’t evidence-based:

Uncertainty creeps into medical practice through every pore. Whether a physician is defining a disease, making a diagnosis, selecting a procedure, observing outcomes, assessing probabilities, assigning preferences, or putting it all together, he is walking on very slippery terrain. It is difficult for non physicians, and for many physicians, to appreciate how complex these tasks are, how poorly we understand them, and how easy it is for honest people to come to different conclusions.

In another post, commenter Iqbal also quotes Eddy and makes a similar argument:

I would suggest you Google Dr. David Eddy and check what he has to say about the evidences used by doctors (He invented the term evidence based medicine). Homeopathy is completely evidence based.

Acknowledging uncertainty in medical care is no secret, nor are the harms from medications – I’ve blogged about both before. And claims that medicine isn’t evidence-based are usually disingenuous. (Science-Based Medicine contributor David Ramey addresses this in the superb “The Evidence for Evidence-Based Medicine.”) But here’s where we come to the tu quoque, and how it’s used as a distraction in an argument: Problems with real medicine does not make homeopathy work! Steven Novella sums it up well:

Mainstream medicine is based upon a culture and institution of science, and a science-based standard of care. The execution of this standard is flawed, but the principle is clear. CAM is not based on a science-based standard. It, in fact, seeks to subvert and even remove the science-based standard of care. And CAM proponents live in a culture of pseudoscience, not legitimate science. To the extent that the science-base of modern medicine is not adequate the proper response is to improve the science (a never ending task), not to use methods that are even less science-based. CAM is largely devoid of science. CAM proponents, to borrow an excellent turn of phrase, use science as a drunk uses a lamppost – for support rather than illumination.

When you see the tu quoque fallacy used, it’s a sign of desperation – unable to respond to the question at hand, the user has decided to attack something else. Even the author of the original post, Dr. Des Spence, used a tu quoque, to defend his argument:

The saga of COX-2 drugs and the unethical, illegal behavior of Merck are real issues in medicine, but are irrelevant to the topic that was under discussion: The ethics of deceiving patients by giving them sugar pills. Vioxx does not make homeopathy ethical! The solution to ineffective regulation and criminal behavior is to fix the problem and do it better – not to decide to abandon science for magical thinking about vitalism. Science standards are equally applicable to all health interventions. And a single scientific standard should be applied to everything – we should not accept a lowered bar for safety and effectiveness just because something is “Eastern”, “Alternative”, “Holistic”, “Individualized”, “Integrative” or whatever buzzword you wish to attach to your preferred form of pseudoscience.

Tu quoque is very similar to the thalidomide gambit (Gavura’s rule), which can be paraphrased as, “Where’s your science now?” There is also overlap with the “Fallacy of the Perfect Solution” aka “Nirvana Fallacy” – that because medicine isn’t perfect, that science advocates have no right criticizing alternative medicine.

Brace Yourself

Physician and author Ben Goldacre has a new book out, a follow-up to the excellent Bad Science. This one is called Bad Pharma, and judging by the excerpts, promises to be a detailed analysis of the behaviour of pharmaceutical companies. I’m interested to see what he recommends to improve the practice of medicine. While I haven’t read the book yet, I doubt Goldacre concludes it with, “Therefore homeopathy works.” But that doesn’t mean you won’t see this argument from others. Science advocates should be prepared for a lot more tu quoque statements.

More reading on tu quoque

Fallacy Files: tu quoque

Your logical fallacy is: tu quoque

Science-Based Medicine: Science, Reason, Ethics, and Modern Medicine Part 1: Tu Quoque and History

Photo from flickr user insert_user_name used under a CC licence.