Contrary to what many believe, neither rational inquirers nor scientists claim to know the absolute truth on matters. They claim to hold provisional truths: answers that are the best explanation for things at the present time.
Of course, this leads to the fact that some, many, or even all of these provisional truths may be wrong. Those with unusual or unaccepted ideas often use this fact to lend weight to their claims. Their argument broadly states: “Absolute truth cannot be known, so no idea can be considered to be absolutely right; therefore all ideas are equally valid.”
It seems logical, but there's a catch. If truth is taken as an absolute (something is either true or false), it means that there's only one possible way to be right, but where the argument falls down is that it fails to recognise that there are lots of ways of being wrong.
Their mistake is that they are basing their thinking on 'black and white' logic; where things can only be true or false, on or off, "1" or "0". To apply that logic to most situations creates a false dichotomy by excluding other possibilities that exist.
There are many ways of being wrong
What we need to understand is that we can be wrong to varying degrees. Let’s say a man has robbed a shop and police ask witnesses for the robber’s height. They could get answers such as 5’ 10”, 6’ 0”, and 1’ 8”. If the robber was 5’11” they are all technically speaking wrong; but the police chief who doesn’t understand that there are degrees of being wrong will not stand much chance of catching his man if he sends his force out looking for a 20-inch armed-robber.
There are many complex areas of inquiry and finding answers is not easy. Initial ideas and hypotheses may be quite wrong; however, where they are shown to be wrong, they will be amended and re-tested. In this process, what happens is that an absolutely true answer may not be found, but we get closer to what is true every step of the way by being less wrong than before.
By rejecting theories and hypotheses that can be shown to be false and replacing them with others that stand up to attempts to prove them wrong (Note: not attempts to prove them right. See: confirmation bias fallacy), we can accept them as being provisionally true. Truth, by definition, could never be shown to be wrong. This is why a scientific theory that cannot currently be shown to be wrong is accepted as provisionally true.
To argue that science can’t prove things to be 100% true is fine, but for people to use it as an argument to give validity to completely untenable ideas is fallacious. Both their ideas and science may be wrong; but science is highly likely to be far less wrong than they are.
When people resort to the "science has been wrong before" appeal, it most likely means that their position is wrong.
An example of its usage
A commonly used example of this fallacious 'science has been wrong before' reasoning is where promoters and supporters of alternative or natural remedies attempt to justify their position by claiming that medical science is 'the system that gave us Thalidomide'.
This claim, of course, creates:
- A false dichotomy.
One has a choice between a system that gave us Thalidomide or a system that is (allegedly) benign. This is a false dichotomy because conventional medicine is not one single approach to healthcare (unlike most alternative systems), it's an eclectic system of healthcare that assimilates any practice that can be proven to work.
- A hasty generalization fallacy.
Conventional medicine, surgery, etc., sometimes go wrong and cause more harm than good. Therefore, all conventional medicine is bad.
- A 'perfect solution' fallacy.
Our alternative medical system does not kill people or cause side effects, therefore it is the perfect solution to imperfect conventional medicine.
The perfect solution fallacy also includes the assumption that the alternative medical system under consideration actually does some good. Many alternative medical systems, and homeopathy is a prime example, are perfectly safe to use and have no physiological side effects: the reason is that they don't actually do anything physiological - good or bad.
The biggest flaw in this type of reasoning however, is that it ignores the fact that there are many ways of being wrong. The assumption is that showing 'science has been wrong before' adds weight to the counter-claim being made; such as: medical science gave us Thalidomide; homeopathy has no side effects - therefore homeopathy is a better medical system than evidence-based medicine.
The truth is, demonstrating that science has been wrong in the past adds absolutely no weight at all to a counter-claim. As there are many ways of being wrong, the counter-claim could also be wrong (!)