What signals the shift to the flat picture plane in Picasso and Braque?

[Jeffrey85]

I’ve been trying to understand the shift in early 20th century painting, specifically how artists like Picasso and Braque moved from their earlier, more representational work into that fragmented, multi-perspective style. I get the basic idea of breaking down forms, but looking at something like "Les Demoiselles d'Avignon" compared to a later analytical piece, I struggle to pinpoint where the depiction of objects completely gave way to the emphasis on the flat picture plane itself.

[Brian.R]

With Les Demoiselles d'Avignon you still feel bodies and a room, but the more I look, the more the line shifts. In the early work the forms sit in relation to space, but in the analytic phase the forms collapse into overlapping planes and the flat picture plane becomes the argument rather than the scene.

[IsabellaNR]

I did a little hands-on check: cut out a couple of cups on card and drew them from one angle, then from another, and stacked the drawings. Depth collapsed and the edge lines started to feel more honest, like the painting was testing what a single perspective can do.

[Ella_L]

Is it possible that the problem isn’t the shift itself but what we expect to see in a painting when we look at it?

[Michael81]

I keep noticing Braque's later pieces feel like grids you can't rest on, and I wonder if the rough edges and visible brush work were part of resisting a neat illusion rather than a technical detail.