It's quite difficult to write about photography as a photographer. A lot of better photographers than me have declined to do it.

What people that are professionals in the art world - both in literature and the other arts - always try to do is to recognize the feasibility of making the transition from the particular to the general - to make the transition from the portrait of one postman - to take Van Gogh, for example, to something that is every postman. That synecdotal transition that most selfies don't make. But we who live in this world, and not simply in our private realities, understand that that's the transition our art has to make.

We sort of understand how painkillers work. You take one, and it reduces your headache. We don't understand how photographs work. And that, to me, is an essential problem as a practitioner.

As humans, we need to question all these notions. What does freedom mean for us? What are our responsibilities? It takes one-250th of a second to take a photograph. So I have the whole of the rest of that second - and of that day - to think.

In the documentary impulse, two species of 'fact' exist side by side: one is coolly objective and the other is fraught, diverse and emotive; one figurative, the other abstract; one prosaic, the other poetic; one factual, the other romantic.

I have a huge respect for the dedication that many people have, on the other side of the Atlantic, to photography. You can count them on one hand here. There's less respect for a Magnum photographer in Britain than there is in America. It's a much more postmodern culture here.

There was a time, right up until the end of the Second World War and beyond, when white people in Europe thought that they basically owned the world and that everybody else was a sort of servant, or a curiosity, or whatever. And that informed 99 percent of the photographic practice that was done. Without being able to address that, I felt I would have failed in my attempt to explain what the urge to document is.