Perceptual/Cognitive Models Made From Purely-Speculative Explanations
Some sketching...
If there is no supporting evidence for a belief, then a belief that it's true is pure speculation. We can denote beliefs with no supporting evidence, and any claims expressing them, as being purely-speculative.
If I don't know what is currently in my laundry, and I say that there is a pink elephant in it, I have no reason to believe that this is actually the case and I am making a purely speculative claim.
It's often hard to say a purely-speculative claim is wrong -- how do I know that there isn't an elephant in my laundry right now? -- but if we can see that the claim is purely-speculative then we are unlikely to give it much credence.
We might expect that it'd be obvious if a claim was purely-speculative, but in fact I don't think that's always the case. I think that it is less obvious when the purely-speculative belief is an explanation of some phenomenon, and even less obvious when that purely-speculative explanation constitutes our perceptual/cognitive model of the phenomenon.
I think a far greater proportion of our knowledge than is commonly believed is in fact not knowledge in the normal sense, but explanations. Much of our memory is like this. As is a lot of what comes to mind when we want/need to justify something. I think what I'm more concerned with here is the case when we observe a phenomenon and develop an explanation for it. A purely-speculative explanation does not have any supporting evidence. By definition, a purely-speculative explanation will involve some entities or properties or behaviour that we can not or have not seen.
Sometimes this is fairly subtle. There were many purely-speculative explanations of those points of light in the night sky that we know as stars -- explanations in terms of gods, pinholes which light shined out of, etc. We can see those points of light, but of course we can not see them and their context clearly. The explanations invoked invisible things in or associated with them.
Most historical beliefs about the nature of the natural world are purely-speculative explanations.
I think it is harder to see a belief is purely-speculative when that belief is an explanation. Or at least, such beliefs are easier to take on board. Historically, it's clear that people were Damn-Sure about all sorts of purely-speculative explanations. You could probably even say that people hold purely-speculative beliefs with even more vigour than ones that have supporting evidence.
I think part of their appeal is simply that they provide an explanation. This can simplify matters, bring order to disorder. And it can, without too much effort, be seen as a kind of evidence for it -- evidence for its correctness because it accounts for something.
But, you might ask, doesn't the fact that it provides an explanation actually give it some level of credence? That seems to be a fairly widely held belief, but history shows that purely-speculative explanations are much more likely to be wrong than right.
In fact I think it's quite easy to come up with a false purely-speculative explanation. To account for the phenomenon it just needs to invoke entities/properties that "just are". That is, some sort of essence. Often, this involves intentional agents of some sort. Why does the sun move across the sky? Because there's a god who pulls it across with his flying chariot. Intentional agents that just do stuff are a commonplace occurrence in our everyday lives, and from that it can seem reasonable to invoke them elsewhere.
I think that once we get used to an explanation, it can be come habitual, and we can start to transparently think of the phenomenon in terms of that explanation. It can become an integral part of our perception of the phenomenon.
An explanation is buried most deeply when it essentially constitutes the perceptual/cognitive model of the phenomenon. I think that in such cases it just seems like you know the nature of the item. It doesn't seem be that what you have is just an explanation to account for phenomena, and a purely-speculative one at that (i suppose you could say that it's not just purely-speculative explanations that are problematic in this situation, though I expect they are more common, because if you've got at least some evidence I think you are much more likely to be aware that you're dealing with an explanation).
Our perception is such that we tend to project our perceptual/cognitive models out onto what we -- to use vision as an example -- 'see'. We treat them as part of what is out there, as if we are directly perceiving them.
In vision, we don't really just 'see' some 'raw' image, just blobs of colours at different positions in the visual field, we 'see' a perception of the scene in terms of our perceptual/conceptual concepts. We see lines, objects, depth. We don't just see a face arranged in a particular configuration, we see an 'angry' face. And so on.
We even 'see' hidden things. If we catch part of a coke can, our mind fills in the missing part of the coke logo. We perceive things about people's states of mind from their words and facial expressions. It's all unconscious and automatic. What is completely invisible to us can see to be quite real and 'there' and seem quite tangible to us. (Information, as it is usually conceived, is such a thing -- we can see encodings of information, but no one has ever seen information itself -- and I would suggest that it is purely speculative, but that's another story).
Sometimes our perceptual/cognitive models can actually affect what we perceive. Like when we're reading something in a book or a sign and we actually mistake a word for what we were expecting to see. Analogues of this happen in what we hear. (Note that if we're not consciously on the look out for these misperceptions, we can easily not take note of them when they happen, so we shouldn't necessarily expect that we would be able to recall them having happened to ourselves).
When a purely speculative explanation constitutes our perceptual/mental model of a phenomenon -- whether we have developed it ourselves or picked it up from someone else, or it is innate -- it can become its own justification. We invoke the entities of the explanation all the time as part of our mental descriptions of what is going on. We lose sight of the fact that this is not what the phenomenon is like, but just an explanation, and it becomes simply how we see that phenomenon -- so of course it is right. The belief in its correctness is based on a circular argument.