| Tom: | I believe X |
| Jerry: | X has been examined and is easily explained by a, b, and c |
| Tom: | I accept that a, b, and c explain 99% of cases of X but that still leaves that 1% that just cannot be explained. |
Most people who read about or debate contentious issues will probably have encountered this argument at one time or another. Of course, it's not always stated as 99-1 percent, it may be 95-5 or 99.9-0.1, but the underlying structure is the same: that there is a small number of instances of X that defy explanation; therefore, some alternative explanation is viable and shouldn't be ruled out.
This argument is normally used with unlikely or extraordinary claims (where 'X' could be crop circles, ghosts, large-cat sightings, UFOs, psychics/mediums, etc.) but it can be used with any claim where someone wants to believe an unlikely explanation in preference to more tenable ones. The argument would be pertinent if the person making the claim could actually show that there is indeed a 'one percent' of cases that cannot be explained by accepted means but this doesn't normally occur: the claim is usually simply asserted as true.
The purpose of this argument
It is used to preserve the belief in a particular explanation for a claim in the face of much better, more likely explanations. For example, if someone believes that orbs in digital photos are 'spirit manifestations' but the widely-accepted explanation is that they are reflections from dust etc., then the person may resort to the 'one percent' claim. i.e. that despite the accepted explanation for the vast majority of instances, there is nonetheless, that 'one percent' that cannot be explained...
This argument can be quite persuasive as instead of being confrontational and rejecting rational explanations, the arguer accepts the rational explanations for the majority of cases. This approach gives the impression of reasonableness – a strong weapon in a debate!
However, the 'One Percent Argument' may not be quite so reasonable after all.
The weaknesses of this argument
- Appeal to Ignorance
As the 'one percent' of instances that are alleged to exist 'cannot be explained', when the one-percent argument is used to support an alternative explanation, it is nothing more than an Appeal to Ignorance fallacy. i.e. the idea that we can infer knowledge about something based on our lack of knowledge of it! e.g. “this orb is possibly a spirit manifestation as I can't explain it otherwise.” is equivalent to saying, “I think I know what this is because I don't know what it is.”
If it can be demonstrated (and it's usually not) that there is indeed a minority of instances that aren't explained by the current rational explanation(s), it doesn't follow that therefore any belief- or faith-based explanation is pertinent. - Abductive reasoning
Abductive reasoning is where we infer a probable conclusion based on prior observations or experience. i.e. we choose the most likely explanation for an observation based on existing knowledge. A familiar example is the saying, “if it looks like a duck, swims like a duck, and quacks like a duck, it's probably a duck.” So, if we see a bird that looks like a duck, swims like a duck and quacks like a duck but has a feature that we haven't seen on a duck before, such as a blue head, a reasonable conclusion (using abductive reasoning) would be that it's a 'blue-headed duck'. It would only require alternative explanations if it was ever proved that it's not a type of duck.
The idea that there is an entire group of things that can adequately be explained (e.g. orbs in digital photos) yet there remains a small fraction of very similar things (orbs that may be slightly non-spherical, for example) which occur under the same conditions yet are fundamentally different from the rest is not tenable. A more probable conclusion is that the '1%' is either just more of the same thing or a small variation of the same thing.
Abductive reasoning cannot guarantee that any conclusion is correct but a good reason would be required to deviate from the conclusion suggested by previous observations.
Conclusion
The one-percent argument is most often used as a reasonable sounding way of maintaining a belief in an unusual or unlikely hypothesis or explanation for some phenomenon.
The crux of the argument, however, is whether the arguer can show that the claimed 'one percent' is not just more of the same or a variation of the same. If they can't do that, it's a very weak argument.