If the same circumstances now don't lead to the same outcome, then how can you be sure it did in the 7th century.

The circumstances aren't the same; in fact, they could hardly be further apart. Why would your personal 20th century mentality have any relevant to the decision making process of 10th century monks? Understanding that people act in a specific historical context is elementary to history. This isn't a repeatable physics experiment.

Exactly. And that's my point - and my answer to your other questions. It's not a proof in any way - so why did you make the claim about the past? You're completely avoiding the fact that your original reply was wild speculation. Just as mine are.

But he did it 500 years later. My whole point is that knowledge was gained and tools changed.

That's the whole point: Hals was less rigorous than his predecessors. Rubens and Rembrandt also were more loose in their style, precisely because the Baroque aimed at conveying emotions more than exact representation and thus they would be more free in their brush strokes.

You don't know that! I find it absurd to claim that throughout 1000 years before nobody ever felt like having "free brush strokes" - or any of the other elements you claim would be easy to achieve.

And yet they have the same general style as Van Eyck, who Hockney gives as an example of mirror-and-camera use.

You don't see a quality difference between Brueghel and Eyck?

Are you telling me that they actually visited hell or saw angels who were kind enough to stand still and pose for them? Did he convince the sun to shine out the northern windows, so he could project and trace it.

You obviously don't take a word I say serious. If you would, you would realize I never claimed that everyone always used the camera obscura - let alone for every brush stroke. So I will end the discussion with this reply.

The difference is: You put it into a question of style choice. And I put it as a question of skill. My core point is: If artists would have been able to use realistic expressions, then they would have.

If they were interested in realistic depictions, why wouldn't they have evolved to a point like Van Eyck long before and stagnated then until the technical methods were invented?

That's like asking: if the Romans liked faster travel - why didn't they just invent cars?

There's a clear, gradual developement of realism. Naturally there's some skill involved, the reinvention of perspective for example, but that motivation still came from a renewed interest in the natural world that wasn't there before.

The gradual development is comparable to many other inventions. You go step by step (metallurgy > steel > steam engine > combustion engine > cars) - with many small elements having to be in place (i.e. rubber). None of that is proof that it was a purely cultural sentiment - and that the Romans stuck to horses because it fit their mentality better.

I know that it is very tough for people to introspect how hard it is to draw. People are not aware that they mostly think in symbols rather than in photography-like pictures. You can see that if you give beginners a pen. Their drawings resemble medieval art in sooo many aspects. Perspective, wrong size-relations and strange expressions being the most obvious one. But it's OK, you don't have to entertain the thought. Just don't pretend the cultural mentality idea is an any more substantiated.