A chess game is commonly broken into three phases: the opening, the middlegame (also called the middle game and the middle-game), and the endgame (also called the end game and the end-game). Unfortunately, too often the phases are viewed and presented as distinct and separate from each other; the game is “divided into three water tight compartments: the opening, the middle game, and the ending, each phase being divorced from the rest of the game.” The Art of the Middle Game by Paul Keres and Alexander Kotov (trsnl. H. Golombek), sat p. 16, Section 1, Planning the Middle Game [Full reference provided in the Recommended Readings section]
However, the game of chess is made “more interesting and more difficult” because of the interrelationship between the three phases, and not because they are labeled and presented as being three different aspects. The opening affects play in the middlegame, which in turn affects play in the endgame. [The Art of the Middle Game at page 16]
The relationship is not as linear and simple as that may seem to appear. The choices made by the players through their initial moves for the opening often dictates how the middlegame may be played (i.e., which lines will be available), and therefore also controls which types of checkmates might reasonably be expected to be encountered in the endgame phase. Thus, play must proceed from an “awareness that the opening is directly followed by the middle game and that the choice of the opening variation will have an immense influence on one’s plan of play in later stages in the games.” [The Art of the Middle Game at page 16]
This is why most chess coaches and teachers stress learning pattern recognition for the simple (elemental) checkmates/basic endgames as a primary basic tool for advancing chess playing skills. Doing so helps the beginner and novices to develop a better understanding of why various openings may work or not work in the manner that the player expects and intends. Much too often, beginners and novices are enthralled by being able to checkmate (who isn’t though?), but worse…trying to do so quickly. Great disappointment and confusion ensues more often than not when the player memorizes an opening or variation on an opening that is favorable and expects the rest of the game to proceed and play itself out, but encounters a curve ball (e.g., an unexpected move). A good chess player recognizes the value of understanding the interrelationship between the phases precisely because the expected result of a variation on an opening often is not as clear-cut or as simple to reach as the beginner or novice may believe and wish/expect to see work itself out on the chessboard during the game.
With these cautionary observations in mind, let’s examine the three phases, general principles and rules, and how they interact with each other.