Albert Einstein:
Did the chicken really cross the road or did the road move beneath the chicken? Whether the chicken crossed the road, or the road crossed the chicken, depends upon your frame of reference.
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Aristotle:
To actualize its potential.
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Plato:
For the greater good.
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Karl Marx:
It was an historical inevitability.
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Machiavelli:
So that its subjects will view it with admiration, as a chicken which has the daring and courage to boldly cross the road, but also with fear, for whom among them has the strength to contend with such a paragon of avian virtue? In such a manner is the princely chicken's dominion maintained.
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Hippocrates:
Because of an excess of light pink gooey stuff in its pancreas.
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Carl Jung:
The confluence of events in the cultural gestalt necessitated that individual chickens cross roads at this historical juncture, and therefore synchronicitously brought such occurrences into being.
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Jean-Paul Sartre:
In order to act in good faith and be true to itself, the chicken found it necessary to cross the road.
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Ludwig Wittgenstein:
The possibility of "crossing" was encoded into the objects "chicken" and "road," and circumstances came into being which caused the actualization of this potential occurrence.
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Darwin:
It was the logical next step after coming down from the trees.
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Ralph Waldo Emerson:
It didn't cross the road; it transcended it.
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Werner Heisenberg:
We are not sure which side of the road the chicken was on, but it was moving very fast.
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Pyrrho the Skeptic:
What road? Was there a chicken?
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The Sphinx:
You tell me.
Learn About the Sphinx!

Mark Twain:
The news of its crossing has been greatly exaggerated.
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Howard Cosell:
It may very well have been one of the most astonishing events to grace the annals of history. An historic, unprecedented avian biped with the temerity to attempt such an herculean achievement formerly relegated to homo sapien pedestrians is truly a remarkable occurrence.
Learn About Cosell!

And here are a few more, just for fun!

Dr. Seuss:
Did the chicken cross the road?
Did he cross it with a toad? Yes! The chicken crossed the road!
But why it crossed, I've not been told!

Grandpa:
In my day, we didn't ask why the chicken crossed the road. Someone told us that the chicken crossed the road, and that was good enough for us. And that chicken would have had to walk barefoot five miles in the snow just to get to that road too! They just don't make them like that anymore!

Captain James T. Kirk:
To boldly go where no chicken has gone before.

Jerry Seinfeld:
Why does anyone cross a road? I mean, why doesn't anyone ever think to ask, "What the heck was this chicken doing walking around all over the place, anyway"?

Bill Gates:
I have just released the new Chicken Office 2000, which will not only cross roads, but will lay eggs, file your important documents, and balance your checkbook.

Colonel Sanders:
What? I missed one?