Denialists are people who reject well-supported scientific conclusions by appealing to pseudoscience and using intellectually dishonest debating tactics. Here is an overview of common denialist tactics, and clear and concise ways to counter them.
Tactic: Quoting Scientists out of Context (also called Quote Mining),
Description: This denialist tactic attempts to cite reputable scientific authorities in a vain attempt to prop up their position. However, the quote has been taken out of its original context, thereby distorting the arguments made.
Countermeasure: Find the original quote and post it, explaining how the scientists position and argument differed from the way the denialist tried to present it.
Tactic: Obfuscating Basic Science.
Description: It is unclear if this tactic is intentional or not but many denialists seem to have a very poor grasp of the scientific background. They commonly fail to understand simple definitions, mechanisms and arguments or drawing flawed conclusions from the available evidence.
Countermeasure: Explain the basic science in a way that even a child could understand, anticipating probable objections. Make sure to include reliable sources, while trying to avoid insulting their ignorance too much.
Tactic: Confusing Mechanism With Fact (or How with Whether).
Description: Involves shuffling the cards and trying to portray a genuine scientific debate on how something is occurring as the pseudoscientific notion that that scientists are still debating the merit of the idea. A classic example is creationists who falsely characterize the debate between the modes and mechanisms of evolution above the species level as if it questioned whether common descent was reasonable.
Countermeasure: Explain that scientists will always debate the details, but that every sane scientists in that debate accepts the fact, even though they may differ on precise mechanisms.
Description: Tries to make it look like there is a genuine scientific controversy where there is none.
Countermeasure: Explain how strong the science is. Also see “Confusing Mechanism With Fact” and “False Balance”.
Tactic: Playing the Martyr Card.
Description: Instead of replying with solid evidence or arguments, denialists often complain that they are being persecuted by the establishment because, in their own view, they are questioning the dogmatic status quo. Comparisons with Galileo or Einstein are extremely common.
Countermeasure: Explain that criticism is not the same as persecution, that science thrive on overturning old ideas and replacing them with ideas that better fit the evidence.
Tactic: False Balance.
Description: Tries to exploit fairness by pretending that there are two different positions, yet equally valid of attention. Teach the controversy, hear both sides and equal time are common manifestations of this tactic.
Countermeasure: Explain that just because two positions are expressed with the same level of confidence does not mean that the truth lies in between. Sometimes one side is just wrong, especially if it is not supported by the evidence. Point out that it would be unfair to listeners if it was pretended that ignorant and dangerous pseudoscience was presented as fact.
Tactic: Conspiratorial Thinking.
Description: In order to explain away embarrassing facts or problems, a conspiracy theory is proposed, which not only lacks evidence but is absurd on many levels.
Countermeasure: Explain that it is a bad idea to attribute things to malice that could equally well be explained by human ignorance or stupidity, that something would have leaked by now or that results would have been too unpredictable and the cost of failure too large for the risk of carrying it out to be worth it.
Tactic: Single Study Fallacy.
Description: Using new and speculative research that has not yet been substantiated or repeated to overthrow and established scientific paradigm.
Countermeasure: Explain that a single study demonstrates nothing and that reasonable conclusions needs a convergence of many different lines of evidence before being accepted, especially where the scientific theory being attacked is solid.
Tactic: Blowing Honest Errors out of Proportion.
Description: Appeals to a discovered error in a scientific discipline and make it appear as if this questions the entire project.
Countermeasure: Point out that honest errors made by individual scientists do not undermine the credibility of the discipline and that the reason these errors where discovered in the first place is because of the self-correcting nature of science. This speaks to the strengths of science, not its weakness.
Tactic: False Experts.
Description: Appeals to the alleged scientific authority of an individual, when this individual is, in fact, not an expert in a relevant field or has a history of anti-scientific denialism. Can also come in the form of providing petitions like the Dissent against Darwin, Scientific Reappraisal of the HIV-AIDS Hypothesis, Oregon Petition and others.
Countermeasure: Point out that the individual in question is a false expert, and provide supporting documentation and references that such is indeed the case. It is also useful to counter with real experts or assessments of how large the scientific consensus on the issue is.