The Snapshot
A chess board sits on a table. Eight rows, eight columns, sixty-four squares. Thirty-two pieces stand in their opening positions. White's pawns form a wall across the second rank. Black's pieces mirror them from the other side.
Nothing moves. The room is empty. An hour passes. A day. A year.
The board remains exactly as it was.
What Is State?
If we were to photograph this board, we would capture everything there is to know about it at this moment. The photograph tells us:
- Where each piece stands
- Which squares are empty
- The arrangement of colors
- The geometry of potential
This photograph is what we call state---a complete description of how things are at a particular instant.
| Natural Language | Notation |
|---|---|
| The board's state is the position of all pieces | state: position of all pieces |
| Each piece has a position | piece: has position |
| Each position is a square | position: (row, column) |
State answers the question: "What is true right now?"
Not "what happened" or "what will happen"---just "what is."
A Minimal Description
How much do we need to describe the board's state?
We could describe it in words: "White's king is on e1, white's queen is on d1, white's rooks are on a1 and h1..." But this is tedious.
We could use chess notation: the starting position is always the same, so we might say "initial position" and everyone understands.
Or we could describe it structurally:
board:
a1: white rook h1: white rook
b1: white knight g1: white knight
c1: white bishop f1: white bishop
d1: white queen e1: white king
a2: white pawn ... all white pawns ...
a8: black rook h8: black rook
... and so on ...The key insight is this: \concept{state is information, and information can be represented in many ways}. The board doesn't care how we describe it. The description is for us.
Beyond the Pieces
But wait---is the position of pieces everything about the game's state?
Consider: whose turn is it?
In the starting position, it is white's turn. That is part of the state, even though you cannot see it by looking at the pieces. The state includes:
| Natural Language | Notation |
|---|---|
| Whose turn it is | turn: white OR black |
| The board arrangement | board: grid of squares |
For now, we will keep our state simple:
state:
board: 64 squares, each empty OR containing a piece
turn: white OR blackThis is enough to begin.
The Frozen Moment
Return to our empty room. The board sits untouched. Does its state do anything?
No. The state simply exists. It does not act, compute, or change. It is a frozen moment---a snapshot.
This might seem obvious, but it is profound. The state has no will. It does not want to change. It is inert, passive, still.
If we want something to happen, we must look beyond the state itself.
We must ask: what causes change?
Try It Yourself
Before moving on, consider these exercises:
Try It Yourself
5 exercises to practice