Imaginary Evidence

Does the fact that we can imagine something provide any evidence about it?

The practice of philosophy and some other disciplines ends with the use of the imagination as a source of argument. As soon as you leave the realms of imagination you are doing science, which is a discipline that begins by testing ideas by systematic observation (evidence), controlled experiment (evidence) and/or Bayesian reasoning (evidence). Or you’re doing natural history, which isn’t testing ideas but observing reality (evidence) in meticulous, systematic detail.

Science uses the imagination to motivate arguments, and to help us along the paths of reason by getting imperfect glimpses of the way ahead, which often lead us off the edge of a cliff we don’t carefully check the footing (evidence) every step of the way.

But evidence is hard and imagination is easy. Imaging often feels like we are learning something about reality outside our heads. But are we?

Is there any reason to believe we are?

Remember what evidence is: it is something that affects the plausibility of a statement.

And remember there is no such thing as “scientific” evidence, because that would imply there is also “non-scientific evidence”. There is only evidence. Science isn’t some special magic thing that takes place in world that’s separate from ordinary reality. It’s just something people do.

We always start with some idea of how plausible a thing is. “It just seems to me”, we say, “that dogs being able to talk is pretty reasonable.” We can give numbers to this: things that are really, really plausible are near 1.0 and things that are wildly implausible are near 0. We can never actually reach “true 1” or “true 0” because that would be imply a belief that could never by changed by any amount of evidence, and if it can’t be changed by evidence it can’t be reached by evidence.

And who would want to believe something without evidence? Can you imagine how stupid that would sound? “I don’t have any evidence for this, but I believe it and will never change my belief.” No one would say that! I can’t imagine it, so it can’t possibly be true. Or can it?

This is the thing about imagination: it doesn’t seem to have anything to do with how plausible something actually is.

We update our beliefs using a simple ratio: the plausibility we should give an idea after we’ve seen some evidence is the plausibility we gave it before seeing the evidence, times the probability of the evidence if the belief is true, divided by the probability of the evidence occurring just randomly.

So if some evidence is really likely if a belief is true but really unlikely otherwise, the plausibility of our belief should go way up. We all start with different initial plausibilities, though, so some people (skeptics) will take a lot more evidence to be reasonably convinced of something than non-skeptics. This is right and good: plausibilities are subjective, probabilities are objective.

This creates an interesting question: does the fact that someone can or cannot imagine something constitute evidence for or against it?

The belief that “I can imagine X” makes X more plausible and “I can’t imagine X” makes X less plausible is extremely widespread. Entire fields of intellectual endeavour depend on it, particularly in philosophy.

This is a general question, and one that can be subject to empirical investigation. Take any statement that is known to be highly (im)plausible. Present naive subjects with the task of imagining that statement is true or not. See if there is any difference in their ability to imagine things depending on their consensus plausibility.

My bet is that if anything, what we can imagine easily is slightly anti-correlated with how the world most plausibly is. But what I imagine is not really relevant, until we have some evidence that what we imagine is evidence. Which we do not currently have.

About TJ

Scientist, engineer, inventor, writer, poet, sailor, hiker, canoeist, father.
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