Mirror images and the observer

Why does a mirror image seem reversed left-to-right rather than top-to-bottom? The opening gives us an explanation that includes the viewer. When we turn from an object to its reflection, we ordinarily rotate our field of sight around a vertical axis. The apparent reversal is relative to our position and orientation. The important relationship is between how we view the object directly and how we view its image.

That is the field-of-sight explanation. We do not need to turn the first paragraph into a physics calculation, but we do need to retain its key feature: the observer's movement is part of the explanation. The author will come back to that requirement at the end.

The second paragraph introduces a different account. Imagine a chair facing a mirror and picture another chair inside the mirror facing the original. This front-to-back explanation treats the reflected chair as though it were a real, three-dimensional counterpart. The author immediately identifies that as the false premise. There is no second physical chair occupying the apparent space behind the mirror.

Still, I can see why the image is tempting. Looking into a mirror can feel like looking into another room. The author wants to explain that appeal without accepting the account as a complete explanation. Something can fit our intuitive way of picturing a situation and still rest on a mistake.

The next paragraph explains the habit behind that intuition. We normally deal with mental representations of objects rather than continually examining the raw sensations from which we form them. When you see a familiar bottle, you simply recognize a bottle. You do not usually stop to separate the incoming visual information from your understanding of the object. Ordinarily, the representation and what we perceive correspond reliably enough.

Mirrors create a problem for that shortcut. We interpret a flat surface as if it opened onto a space with depth. Notice where you focus your eyes: usually into the apparent space, not on the surface of the glass itself. That example helps make the abstract distinction concrete. The image can look like a three-dimensional object even though, on the author's account, treating the reflected chair as another real chair is a mistake.

There is also a scientific reason the front-to-back account appeals. It seems to explain what the mirror does without bringing in what the observer does. Scientists traditionally prefer to separate a phenomenon from the person observing it. That preference helps explain the attraction of an account focused on the mirror alone.

But the author says that approach leaves out something essential here. We are trying to explain how an image appears. An appearance has a viewer and a point of view. Remove the viewer entirely, and we have stopped explaining the experience that prompted the original question.

The final paragraph states the requirement directly: an adequate account must consider both what the mirror does and what happens when someone looks into it. That brings us back to the opening field-of-sight account, which explicitly includes the observer's orientation and movement. The main point is therefore more than a rejection of the front-to-back explanation. The criticism shows why a satisfactory explanation must include the mirror and the observer together.