PART 1 • A tree of possibilities
We call that big ol' batch of potential moves the “chess tree”.
And I'll bet you're dying to know why aren't you? I'm glad you
asked. Have a look at this (very small) example which occurs
after the moves 1.e4 e5 2.Nf3 Nc6 3.Bb5 a6:
These are the initial moves of the Ruy Lopez Exchange Variation (and
don't worry if you can't read algebraic chess notation – I'll teach you how
in Part Two of this book). White plays 4.Bxc6 (that move is what makes it
the Exchange Variation). Black has a lot of moves he can play next, but
only two which make any real chess sense; White has a few good replies
to both of Black's moves. If we start reading the diagram at the bottom
(with 4.Bxc6), then add Black's replies above it, then add White's replies
above Black's, and connect them all with lines, we get something that
looks very like a tree. That's why it's called a chess tree (and you'll often
hear chess variations called “branches”, and hear a position at the end
of a variation called a “leaf node”. It's a wonder that chess analysts aren't
called “gardeners”, for crying out loud).
CRUNCHING THE NUMBERS
When we talk about evaluating a chess position, we mean looking at the
board (with knowledge of which side is to move – that does make a big
difference!) and figuring out which player currently has the advantage.
We all do this all the time when we play chess. We look at the board,
figure out who's ahead, and then we start looking at candidate moves,
figuring what the opponent might do in reply to each of them, then what
we'd do next, and then we decide who's ahead (“If I do this, he'll do that,
then I'll do this – who's ahead then?”). It's a little more complicated than
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