Stage 1: Non-Objective Fragmentation
Upon Abstract thought activating, the person's body within the building become crudely-made 3D structures like that of a Picasso painting.
Stage 2: Deconstruction
The person's body begins fragment into separate sections to break down and fall apart.
Stage 3: Two- Dimensionalization
A while after Stage 2 is complete, the screen squeezes in on the character into a slim vertical line, and when it expands, the character becomes simple 2-D drawings.
Stage 4: Non-Figurativity
Then the person enters the final stage, where they become nothing but single-colored geometric shapes of their bodies. It is unknown, however, that if people might become unforgotten in this stage, as it doesn't show.
Eventually, the person has to be quick to escape to the exit of Abstract Thought. Some solutions, during Stage 4, are a better idea, like Sadness told Joy and Bing Bong to fall flat on their faces, which made a line replacing the shapes, to exit.
Role in the film
While trying to find the path back to the headquarters, Joy and Sadness encounter Bing Bong, who tells them he knows a shortcut for arriving to the Train of Thought. However, the shortcut, which happens to be Abstract Thought, is dangerous, even displaying a sign that says to keep out. However, due to Bing Bong's illiteracy, he thinks it's safe to go in. Seeing Bing Bong walk in with no problems, Joy and Sadness proceed to follow.
When two mind workers arrive to Abstract Thought, one of the workers notices something moving inside, so she activates Abstract Thought to get rid of it. With Abstract Thought turned on, everything in the building begins floating. At that moment, Joy, Sadness and Bing Bong start to suffer through the four stages:
- As Joy, Sadness and Bing Bong figure out what's happening, their bodies become Picasso-esque blocky structures. As Joy asks what's happening, Sadness tells her that they're going through the four stages of abstract thought, and they're just in the first. Bing Bong tells them stay calm and keep together. However, just as he finishes his sentence, his left arm falls off.
- The three heroes' bodies begin to break down and fall apart. With that happening, Joy, Sadness and Bing Bong attempt to make a run for the exit while struggling to hold their bodies up. Sadness quickly tells them that if they don't escape, they're going to be trapped in Abstract Thought forever as nothing but shape and color. When Joy questions Bing Bong why they entered in Abstract Thought, he just replies by saying it's a shortcut. Moments later, the train arrives.
- As the three make a run for the exit, the screen squeezes in on them, and when it expands, the three characters are now 2-D drawings. No matter how fast they're running, they're not moving. It turns out the reason they aren't moving is because of the lack of depth (because they're 2-D figures). Joy, Sadness and Bing Bong climb up to the exit's floor level, but they're too big to fit through the small exit.
- The three then enter the final stage, where they become nothing but single-colored geometric shapes (Joy is a yellow 8-pointed star, Sadness is a blue tear-shaped blob, and Bing Bong is a tall pink, trunk-like figure).
When Bing Bong declares that they aren't going to make it out in time, Sadness becomes a thin line by falling on her face. She tells Joy and Bing Bong to do what she's doing so they can slither out the door, and they proceed to do so.
The three successfully make it out of Abstract Thought just in time. But, unfortunately, it was too late, as the train has just left. With the three out, they begin to revert back to their normal selves. Luckily for them, another train station was nearby, right inside Imagination Land.
- Joy and Sadness' appearance during Stage 4 appears to be a reference to their performance models (Joy being a star, and Sadness being a teardrop).
- Docter comments that Abstract Thought would be one of the newest constructions in Riley's mind, as in real life it develops around age 10. This could explain how Bing Bong had passed through it safely numerous times before, it having never activated.
- The only object that went through all of the stages, but had its own shape and color in the fourth, was the imaginary bag, which was represented by a purple triangle.