Tag Archives: hidden


The Ebbinghaus illusion: two orange circles, one surrounded by large blue circles, the other surrounded by small blue circles

The Ebbinghaus Illusion.

Previous post: Introduction.

Note: Most of the ideas here are developed further in my 2018 book, Philosophy of Time and Perceptual Experience.

As an example of what I’ve been developing about this subject, here is what I think is necessary in order for something to be an illusion. The implications are significant, and will feed into the rest of the work.

Three conditions of illusion

I think this: to get an illusion, at least three conditions must be satisfied:

  1. The phenomenological condition: for there to be an illusion of something (x) there needs to be an appearance of x. E.g., in the Ebbinghaus illusion above, the two orange circles appear to be different sizes.
  2. The metaphysical condition: there needs to be a way things are — a way things actually or really are. ‘Possibly’ isn’t enough; neither is there being a way things are believed, imagined, hoped, etc., to be; that is, it is not enough that for an illusion that things are merely intended to be (in the broadest sense of ‘intended’). E.g., in the illusion, the two orange circles are really the same size (and it is not just that we believe or think that they are the same size).
  3. The discrepancy condition: The appearance of x must fail to correspond to reality; there must be a discrepancy between, how things seems and how things (actually or really) are. That is, how x is described under the phenomenological condition does not correspond to how things are described under the metaphysical condition. E.g., there is a discrepancy between the apparent size of the orange circles and the real size of the orange circles.

Remove one of these conditions, and there is no illusion.

— If x is in no way apparent to you, e.g., if it is hidden, or too small to see, or too light to feel, or too far away and too quiet to hear, then there can be no illusion. You can of course make a misjudgement about it anyhow: believing it is there, and being correct that it is, you might still think it is some way that it is not. Someone tells you that your brother’s car is in the garage; you remember your brother’s car is yellow, and so judge/imagine/expect etc., that there is a yellow car in the garage. But your brother re-painted his car and it is now red; so you make a misjudgement, you imagine wrongly, your humble expectations will not be met. Wrong as you are, you are not here under an illusion.

— ‘2’ is the most difficult one for me, at least, to remove in the definition. This is because I am what some philosophers call a ‘realist’. I hold that there is something the way the world is independent of what I or anyone (at all, anywhere, ever) believes, hopes, intends, represents, etc. of the world. This does not preclude my beliefs etc. corresponding to the way the world is (otherwise I might be a skeptic, or some variant of skeptic at least) ; nor do I know how I came about my beliefs about the world; nor am I clear how I could justify such beliefs. But I do think that the world is a certain way, no matter what I think.

Others might have other views, and deny that there is a way the world is. Or, they might refuse to engage with such an assertion, sticking perhaps to how things seem and one’s beliefs, and leaving it at that. If so, I do not know why they would ever assert cases of illusions. My uncertainty comes of this: given only appearances without any idea of reality, then something appears to be some way; but, one cannot say if it is that way (because the world isn’t one way or another). So, how can this appearance be — or not be — illusory? One cannot set up the next condition because one cannot say that appearances are mere appearances, fail to match how things are. So what is left to make a case for there being an illusion?

— ‘3’ requires a discrepancy. Remove the need for the discrepancy and I cannot see any reason to hold that there is an illusion. Say one  removes it because one refuses to engage with one of the relata of the discrepancy: one refuses to say how things appear or how things are; or perhaps one does not have an opinion on either or how they are related. In that case, I do not think that one can assert that there is an illusion  — or that there is not an illusion, for that matter. All that can be said is how things seem, or instead how things are, but not both. But I think we do talk about both — even, in fact, particularly in scientific practice — and especially in gathering evidence of illusion and ‘meta-cognitive error’ (which I’ll talk about later). That I’m correct or not about this is one discussion I’m interested in having from this research.

Other philosophers add further conditions, to which I’ll turn to soon in a post. But even at this stage, I think that there are interesting implications for saying that there are illusions of time.

Next posts:

1. First steps: time and the metaphysical condition of illusion

2. Conditions of Illusion II