Letty wrote:Portal Star, explain a little more about "intellectually stimulating."
Imagine that you're living in a time when pictures are nearly always (99.7%) simulations of three dimensional space.
These pictures do their best to encapture light, shadow, and color in a way that best emulates this space.
The impressionists start to break up the image a bit, but don't leave the image. They are sill catching a moment in time and trying to sculpt it onto flat canvas - like a photograph.
Then you have Duchamp, who (and I'm not trying to give him singlehanded credit for these ideas, but for the sake of argument I'm speaking only of him) introduces a painting that is not a single moment in time. You have never seen anything like this before. It is radical - not only is it not a clear depiction - it is not a still depiction. It shows in one still frame a figure in motion. This blows your 19th-20th century mind.
A new element has been introduced into the frame - time. It had been eluded to, it had been symbolized. But it had never (as far as I know) been pained into one simultaneous moment. This is intellectual because it shows an awareness of time which may now, in out time, seem trite - but at the time was revolutionary.
Sometimes you simply have to look at paintings in their historical context.
The history of art isn't one of progress - it isn't a linear path, but it is steps of action and reaction.