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{{slides|See [[Depth and Perspective]] for slides.}}
==Ambiguity and Impossibility==
[[Image:necker-cube.gif|thumb|right|Necker cube]]
The Nekcer cube is an ambiguous figure, it has two possible interpretations as a three dimensional object.  In fact, all flat images can have two interpretations, though most of the time there are enough depth cues to force the viewer into one.

Vasarely's ''Kocka'' from 1973 and Escher's [[escherwiki:Convex and Concave]] are good examples of ambiguity in art.

[[Image:Vasarely-Kocka-1973.jpg|400px]]

When depth cues in one part of a picture conflict with depth cues in another part, the three dimensional scene is impossible to construct, and we have an impossible figure such as the [[wikipedia:Penrose Triangle]] or this impossible cube:

[[Image:impossible-cube.jpg]]

Some suggestions for things to do with students:
*Identify ambiguities
*Draw impossible figures
*Identify impossibilities
*Be specific: There are two trumpeters in Convex and Concave. Describe what would happen to each of them if they both jumped out their window.
*Goal: Have students look critically at art.

==Art is Illusion==
Escher and Rene Magritte force the viewer to acknowledge that they are looking at a flat picture.. art, not reality.
Some good examples are Escher's [[escherwiki:Dragon]], [[escherwiki:Three Spheres]], [[escherwiki:Doric Columns]], and Magritte's [[escherwiki:The_Treachery_of_Images]], [[escherwiki:The Human Condition]].

One could take this farther by looking at optical illusions and Op Art.

==Resources==
* [[escherwiki:Flatness Exploration]]
* [[escherwiki:Impossible Exploration]]
* [[escherwiki:Impossible Exploration II]]
* [[escherwiki:Impossible Figures and Escher Exploration]]