Van Lier's philosophy of photography is typical of non-photographing philosophers philosophising about photography. The language, the confusion, the jargon, the irrelevant tangents, and the misunderstandings are echoed in similarly arcane outpourings from Jean Baudrillard, Jacques Derrida, Roland Barthes, and even Susan Sontag.
It's many years since I was paid to do philosophy and in the interim I have made a full time career in photography.
Since there seems to be a lot of anxiety about reality I would offer the observation that there IS something particularly realistic about a photograph that separates it from virtually any other kind of representation. A photograph is generated when a physical sample of subject matter travels across space (at 300 000 Km/sec!) and penetrates the sensitive surface, lodges in it, and occasions changes that result in marks. This arrangement of marks, if it coheres as a picture, is a photograph.
A number of corollaries follow.
Only real things are capable of delivering physical samples. Photographs cannot be made of imaginary things, past events, or things that have not yet happened.
A photograph and its subject must simultaneously exist in each others presence for the physical connection to be possible. A photograph confirms the existence of the subject. A subject is a necessary (but not a sufficient) precursor to a photograph.
A subject that gives off a physical sample of itself gets lighter. A film receiving an exposure gets heavier. For the record a 8x10 sheet of 100 ISO film absorbing a middling exposure (zone V if you like) experiences an increase in mass of about 10 to the minus 24 kilograms. All of those kilograms come from the subject. This mass does not sound like very much but it is incomparably greater than nothing at all. And if that 10 to the minus 24 kilograms hit you in the eye you would surely feel it. After all it arrives with a muzzle velocity of 186 000 miles per second.
At the moment of exposure the camera rocks backward due to the physical impact of light. The effect is not large but it is not zero. It's a fun calculation. Try it!
One could continue with film getting hotter when exposed, latent images being heavier than no exposure, and so on but the central argument is this: The core of photography lies in an event that takes place in physical reality and many people, not just philosophers, would assert that this physical reality is the only kind of "reality" that actually exists.
Oh, and another outcome is that non-photographing philosophers end up ruminating about their own perplexity and bewilderment rather than the deep values of photography itself. I should think that Van Lier would have done better to sit down and have a good long read of APUG and THEN written his book.