Thread by @michaelzlin

Some people are wondering, with some scientists expressing opposing views about the possiblity of a lab leak in COVID19 origins, how do they know who to trust? In this thread I describe how to recognize the rhetorical devices or fallacies used to push weakly supported views.
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First some background. Scientists face the situation of figuring out the steps that lead to an outcome all the time. For example it’s what molecular biologists do on a daily basis to work out the molecular reactions that underlie initially mysterious biological events.
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We start by brainstorming all the possible hypotheses that are consistent with the known outcome *the more the better* to makes sure we don't miss the right answer. Then we gather data that can help rule out one hypothesis or not.
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Some data could favor one hypothesis over others, but we don’t rule out high-impact hypotheses generally based on a preponderance of data or likelihood. As long as it can still fit the observations, a hypothesis remains in play. The reliability of data must also be weighed.
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In the lab, we can do experiments to gather those data. For COVID19 origins, we (as in humans) can also gather data, if we wanted to. The most relevant to discerning whether SARSCoV2 was passed without or with lab involvement (100% natural vs lab leak), are as follows:
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1. additional virus sampling from the Mojiang mine and caves in Yunnan
2. logs of bat swab specimens collected and viruses cultured and samples disposed by WIV
3. full descriptions and logs of the SARSCoV2 antibody tests performed on WIV staff
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4. hospital records and interviews of HCWs treating the WIV workers hospitalized with flu-like illnesses in November 2019
5. results of virus testing in animals in Wuhan and Yunnan

These data are obtainable but all we have now is the last one, and the results are negative.
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So this is a solvable problem, should PR China wish to provide the data needed to solve it. But right now, it is not solvable with the existing data.
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So given this background, how do you know which scientists to trust, when some say we can already rule out lab leak and others say we cannot rule it out? You can look at the quality of the arguments. If the arguments made are low in quality, the position is weak.
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And some low-quality types of arguments are the following:

1. ad hominem attacks, e.g. calling a questioner names like disgraced or discredited rather than addressing the question

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2. appeal to authority, e.g. “I’m an expert and you’re not” or “this other person who is famous backs me up” without analyzing the logic of their positions

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3. circular reasoning, e.g. Dr. A saying “My position X is backed up by other scientists such as Dr. B and C” but when you ask Drs. B and C, they say “According to Dr. A, and he says it’s X”

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4. straw-man argument, or conflation of opposing arguments, e.g. “Proponents of lab leak say the virus was deliberately engineered, so if we conclude it is not, then all kinds of lab leak can be rejected.”

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5. absence of evidence arguments, e.g. “There’s no evidence of lab leak”. This one especially gets me because the whole point of brainstorming hypotheses is to create ideas to investigate in the absence of evidence.

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6. false non-equivalence, e.g. “There’s no direct evidence of lab leak, so it shouldn’t be considered. On the other hand, we think a route from cave/mine to city via food animals is more likely, even though there’s no evidence of that either.”

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7. appeal to emotion, e.g. “We shouldn’t investigate this question because it would insult someone who is a decent person.”

8. appeal to politics, e.g. “We shouldn’t investigate this question because it would strengthen the political opposition”

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Of these, I think appeal to politics is the most harmful, because rather than even trying to appeal to some common element of humanity, the speaker is trying to appeal to the listener's political desires, which by definition means pushing one group's interest above others'.
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And these fallacies can be combined, e.g. “There’s no evidence of lab leak, so we shouldn’t demand the evidence either” combines lack of evidence + circular reasoning.
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Or “Proponents of lab leak say the virus was deliberately engineered, but there is no evidence of that” combines straw-man plus lack of evidence arguments.
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Or “We shouldn’t investigate this person because it would insult someone decent who didn’t do anything wrong” combines appeal to emotion + circular reasoning/
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Sometimes you can see multiple fallacies in just one article, for example the one @kundan_official astutely analyzed below. It's a valuable lesson in that you need to be use critical thinking about things you read even in brand-name websites.
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https://twitter.com/kundan_official/status/1396113505464373253

It also shows, as did @Ayjchan multiple times, that you don't have to be someone who has led multimillion-dollar efforts on isolating viruses in China, or a writer for a well known publication, to make logical arguments and refute illogical ones.
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So when someone with a PhD says their scientific opinion is something, but then use the fallacies above to push their position or to attack those who don’t agree with them, they are no longer engaging in a scientific discussion.
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On the other hand, a PhD acting as a real scientist will assess the situation in terms of how much we know and how much we still need to know. That is, they will point out a scientific investigation has stages, and describe the degree of certainty possible at this time.
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So for readers who want to know whose *scientific* opinion to trust, rather than whose *political* opinion to cheer, just look for those telltale signs above. They are signs not of strength for their position, but of weakness.
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(aka double-standard fallacy)