Considered materially, in law and games, there are only pieces and the board; the pieces can remain the same while the board changes, as when we take checkers and put them on a backgammon board. Or, the pieces can change while the board remains the same as when we take off the chess pieces and put checkers on the chess board.
Roman jurisprudence says the pieces in the "game" are of two kinds: persons and things, and it defines the board as the actions allowed between persons concerning persons and things. If we add actions between persons and things, e.g. as in admiralty against a ship, then we change the moves on the board while keeping the same pieces. If we remove classes of persons, e.g., modern America’s denying legal personality to families, then we change the pieces. We can alter the pieces as when chess altered the movement of the queen to make it more powerful. Thus, we did when we allowed dead men to bring tort actions.
The Romans were far "ahead" of us in thinking of personhood as determined not by some natural fact about individuals but by the power of the law, as we now treat families and marriage. Thus, they treated some admittedly real natural individuals as lacking personality, i.e., slaves, just as we treat unborn babies. We do the same with some moral corporate personalities, i.e. married couples and families. We treat them as if they were not corporate personalities and had no nature, rights or interests apart from the individuals constituting them.
Thus, legal revolutions can occur with a great semblance of continuity in the sense that the board or the pieces may remain the same, while the game itself is radically changed. In the United States, it may not have seemed like much of a material revolution to declare that unborn babies were not pieces any longer, because the rest of the moves remained the same. Likewise, when we declared that families were whatever we said they were, the board remained the same so things seemed somewhat unchanged. But really we went from playing chess to playing checkers.
Too bad law is not a game.