What happens when we carry a train of reasoning to its ultimate extreme, far past the reaches of sanity to the realm of the patently absurd? Here, we discuss such an argument in informal logic, borrowed from formal mathematical reasoning, and here known as the Reductio ad Absurdum.
In formal logic it may be used to show an argument's claim to be false by following it to its ultimate logical conclusion, revealing a contradiction, an absurdity, or it may be used as a form of Straw-Man argument, known here as the False Reductio. I'll deal first with the latter.
This works by forcing a conclusion that while absurd, doesn't use the actual reasoning of the original argument, such as:
If you're skeptical of the existence of UFOs, Bigfoot, and ancient aliens, then you must also be skeptical of the existence of the Taj Mahal, the Sydney Opera House, and the Empire State Building, since you've never been there to see those places.
This is fallacious because the proportional nature of the claims requires proportional standards of evidence. The criteria for each differ, and the argument itself ignores the use of evidence other than anecdotal testimony and grainy, low-resolution, or obviously photoshopped videos and photos.
Here is one of my favorites:
If you don't believe in psychic abilities then you also disbelieve in dark matter and dark energy, so 90% of the Universe does not exist to you because you haven't seen those either.
Again with ignoring evidence other than personally witnessing something. Also, it fails to consider the fact that though there is some question as to what dark matter and dark energy are, they have been reliably observed by their effects on the visible universe itself, and the evidence shows that they are real. Clearly, elusive supernormal psychic abilities and invisible but indirectly observable astrophysical phenomena are not analogous.
But all is not without a ray of light in the dark. There is an informally valid and intellectually honest use of this as well, to highlight the fallaciousness of some extraordinary claims. Here, the actual train of logic of the original argument is kept intact.
Here are a couple of silly claims I've come across:
The ancient Egyptians could not have built the pyramids without alien or Atlantean help. They were far too primitive a civilization.
In order to know what a human skeleton looks like, the Maya and Aztecs must have been given X-ray machines by ancient astronauts.
Such claims reek not only of thinly disguised racism and colonialist arrogance, but stupidity and historical shortsightedness as well. Typical of most of the claims of pseudo-archaeology, especially where ancient non-whites are not given due credit for their accomplishments.
And skeletons? Come on, that's just silly!
Here, we may apply the same train of logic to what the proponents of these ideas, mostly whites of Western descent, dare not apply it to: historical Europeans:
How could the Medievals possibly have had the intelligence to invent such marvels as the crossbow, stained glass windows, steel armor and weapons, and those massive cathedrals! They had to get their technology from aliens, because they were too inept to come up with them on their own! They must have gotten medical imaging technology from the aliens too, because Medieval art has lots of skeletons in it, and how could they have possibly known what those looked like without using it?
Absurd? Clearly it is, and in retaining as closely as can be the reasoning of the original applied to another subject, it shows that.
A side note: Technology is cumulative, and evolves over time, with earlier, precursor technologies leading to better, more advanced ones, with archaeological remnants to show this progression, no matter the location, or ethnic and cultural makeup of the civilization. This is true even dating as far back as the Paleolithic with stone tools.
Never underestimate human genius. There exists brilliance in every human era, with no need to gift early peoples with technology from super-civilizations for such tasks as constructing even impressive monuments, which require only engineering, tools, and social organization which we know they had, as opposed to the claims of pseudo-historians in massive, and dare I say, monumental, arguments from ignorance.
But I digress.
Reason is a tool. Use it well and it will serve you reliably, leading to the acquisition of more true conclusions than false ones. But abuse it, and the content of the claims you accept and promote becomes much more prone to error. Especially when you misrepresent the chain of another's reasoning for ideological ends.
Tf. Tk. Tts.