Note: Most of the ideas here are developed further in my 2018 book, Philosophy of Time and Perceptual Experience.
In my view, a good explanation — or a good philosophical or metaphysical explanation, anyhow — is a general one. It does not just explain one particular thing; it explains a multiple of things. I think there is a limit to any such explanation, due to the particularity of everyday things, though. The thisness — or however you might put it — of any particular object, e.g., this particular orange, means that explanations of how this orange comes about, and/or accounts of its current constitution, cannot be generalised to all oranges, or even a non-singular sub-set of oranges.
A lot of the individuality of that orange, however, can be captured by simply pointing out its unique location in space and in time. The orange is just like other oranges, except it is at this time and this place.
Still, I think the better explanation is the more general one. It is not the firefighting one, the ad-hoc, we-need-it-now/nevermind-then/nevermind-later. It is also not the one which explains only how this orange came to be on my table, but also how oranges come to be on tables in general.
Similarly, if I introduce a concept of space in order to explain a particular geometric-optical illusion, then it is a weakness of my theory that this concept only covers that illusion, doing nothing for other kinds of experience, illusions, hallucinations or otherwise. It is being introduced ad-hoc, and only specifically for that illusion. In contrast, if I introduce a concept of space which is already there, or can be effectively generalised to other things, then there is nothing ad-hoc about this.
So what concepts of space are there already, which might be used to explain geometric-optic illusions?
What Surrounds You?
Let’s start with your idea of space.
If I ask you, what surrounds you, what will you say?
There are two ways I think I might answer this question.
- First, I might simply describe what I am aware of, aware of without any obvious reflection or mediation. I just look around me, which is so far as I can tell a simple turning of my neck and keeping open of my eyes, and say: there’s this, and this, and so on.
- Second, I might reflect upon it and think about what there has to be and what there can be around me.
‘1’ can be understood as giving a phenomenological description — a description of how things seem. I offer a description even if I am a dying astronaut hallucinating in the depths of a void, i.e., where nothing is around me, but there seems to be something.
‘2’ can be understood as doing metaphysics, i.e., formulating a metaphysical theory or speculating about the metaphysical status of the spatial arrangements of things around me. So, for example, if I believe that I am hallucinating, or am under an illusion, this would affect what I say when asked ‘what surrounds you?’. I would not draw on how things seem to me, since I believe this to be an hallucination or something similar. I might say, in the right circumstances, something like ‘I seem to be surrounded by stars, distant hills, the song of crickets but I am under an illusion’. I’m really surrounded by four illuminated walls in a dark room’.
‘2’ is at least as important as ‘1’ in answering this question. If I answer ‘I’m surrounded by #’ then I don’t mean just what I seem to be surrounded by. I mean what I am surrounded by.
So, with geometric-object illusions, I can describe what I seem to experience and what I think is out there. The illusion is the clash of those: e.g., (from last post) there seem to be uneven lines but the lines are even; there seem to be small circles and big circles, but the circles are all the same size.
So, when I ask you, what surrounds you, what will you say? And in particular, what HAS to surround you? What can’t be surrounding you? And how does this correspond to your experience?
My answer, like many of my answers, is that it depends on how one thinks about time, which requires a lot more detail. For now, we can draw an analogy between the different somewhat live ways of thinking about time and imaginary ways of thinking about space.
Roadrunner: The Painted Tunnel on the Cliffside
Wile E Coyote paints an image of a train tunnel on a sheer cliff side and waits for Roadrunner (and lunch).
Clearly, his plan is: the roadrunner sees what seems to be space stretching into the cliff, tries to run into that space, fails(because there is no space stretching into the cliff), and is knocked out (and becomes lunch),
However, instead: the roadrunner sees what seems to be space stretching into the cliff, runs into that space, does not fail, is not knocked out (and escapes).
Further: Wile E Coyote, puzzled, tries to run after the roadrunner, fails, and is knocked out.
One way to look at the difference here is that roadrunner and the coyote occupy different worlds with different kinds of space in their counterpart areas. In the roadrunner world, space stretches into the cliff; in the coyote world, it doesn’t.
In that case, the apparent spatial extension into the cliff is, in the roadrunner world, not an illusion whereas the apparent spatial extension into the cliff, in the coyote world, it is an illusion.
Something similar can be said of the phenomenology and metaphysics of time.
1. One might be tempted to then say that this is all there is to the ‘thisness’ of any particular orange, or any object. Some metaphysicians do just this; some bundle theorists hold that all there is to an object is the instantiation of properties located at the places and moments in which it exists.
2. For related discussion of hallucination when test pilots are under extreme pressure, see this episode of RadioLab: http://www.radiolab.org/2006/may/05/out-of-body-roger/