The phrase "path dependency" is used to express the idea that history matters--choices made in the past can affect the feasibility (possibility or cost) of choices made in the future. This entry in the Legal Theory Lexicon introduces this idea to law students, especially first-year law students, with an interest in legal theory.
The General Idea of "Path Dependency"
The general idea of path dependency is that prior decisions constrain (or expand) the subsequent range of possible or feasible choices. That is, a decision, d, made at t1 may affect the choice set, S = (c1, c2, . . . cn) at t2. We can define a choice set as a set of actions that a given agent could take. Or to expand the path metaphor, if we imagine a network of paths through time, from past to future, decisions to branch at an earlier point on the chosen path may affect the destinations that one can reach from a later point on the path. Sometimes, if we choose the left fork, we may be able to reach exactly the same destinations we could have reached via the right fork, but sometimes, our choices foreclose some possibilities altogether. It isn't always the case that in the long run, there's still time to change the road you're on.