diff --git a/notes.md b/notes.md
index 67cc9f6..558f630 100644
--- a/notes.md
+++ b/notes.md
@@ -7,12 +7,24 @@ For each, explain how the behavior is accomplished.
 
 ### Checking to see whether the game is over
 
+Responsible class: `TTTGame`, method `is_over`.
+
+Explanation: `TTTGame.is_over` determines whether play should stop. It returns True when the board is full or when either player has three in a row using `check_winner`. The game logic and win/draw detection are implemented on the `TTTGame` class.
 ### Determining which actions are available at a particular state
 
+Responsible class: `TTTGame`, method `get_actions`.
+
+Explanation: `TTTGame.get_actions` inspects `state["board"]` and returns a list of indices for empty spaces (those containing `'-'`). The game class encapsulates available-move generation for the current board state.
 ### Showing the board
 
+Responsible class: `TTTView`, primarily `print_board`, `format_row`, and `format_value`.
+
+Explanation: `TTTView` handles all screen display. `print_board(state)` arranges rows and separators, `format_row` formats a single row, and `format_value` prints an `X`, `O`, or the index for an empty spot. The view is responsible for how the board is presented.
 ### Choosing which action to play on a turn
 
+Responsible classes: `TTTHumanPlayer` and `TTTComputerPlayer`.
+
+Explanation: Players decide moves. `TTTHumanPlayer.choose_action(state)` prompts the user and returns the selected index. `TTTComputerPlayer.choose_action(state)` to use a strategy (here `RandomStrategy`) and returns the chosen move. So the player classes and any strategy objects they use are responsible for selecting the action to play on a turn.
 
 ## Checkpoint 2 Notes