A TREE OF POSSIBILITIES
Every chess position offers endless possibilities. Don't believe
me? Let's set up a chess board, take a look, and consider a
few simple numbers.
• Yep, it's the starting position for a game of chess. White has twenty
possible moves at the game's start (two for each of eight pawns and
two for each of two Knights; 16 + 4 = 20). After any of White's twenty
possible starting moves, Black has twenty possible moves of his own.
Thus there are 400 possible chess positions after just one move by
each player (20 x 20 = 400).
Four hundred possible positions – after just one move for each side.
Wow!
• Now let's expand on that idea. Just as an example, we'll imagine a
position in which White has exactly thirty possible moves (we call each
of these a candidate move), for each of which Black has exactly thirty
candidate moves in reply, after each of which White has exactly thirty
possible replies to each of Black's moves, and so on. Sure, it's highly
unlikely that a position which produces such nice orderly numbers
exists, but that's why I said we need to imagine it. Besides, the initial
position isn't the point – it's the number of positions which come later.
• So we'll imagine that such a position exists. After White makes one
move (which computer chess guys call a “half move” or a “ply” -remember this terminology, it's important), there are thirty possible
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