Play is something we all do--it seems so natural, it feels a little bit ridiculous to ask why we need it. But psychology professor Alison Gopnik explains some profound benefits, and tells us about a noticeable shift that happens somewhere between age three and six—a shift that causes a kind of tug of war between total imaginative freedom and the rules.

Brian Christian, who we talked to for our Talking to Machines show, weighs in on this same philosophical battle with an example from the 1863 World Championship of Checkers, where every single game in the 40-game series was a draw. According to Brian, checkers reached a point where all the best moves were known, and top-notch players realized it was possible to play an ideal game by using a set of plays known as "The Book." And this pretty much killed the game by sucking out all chance for improvisation.

Then, Frederic Friedel, the cofounder of ChessBase, tells us about creating a database that's so widely used his critics call him the "man who ruined chess." But according to Frederic and Bobby Fischer biographer Frank Brady, the sinister studiousness of The Book in chess is counterbalanced by a totally unpredictable realm of possibility known as The Novelty.

Further reading:

Alison Gopnik: The Philosophical Baby

Brian Christian: The Most Human Human

Frank Brady: Endgame: Bobby Fischer's Remarkable Rise and Fall