Historical outcomes are rarely determined by some set of antecedent conditions. Instead, the outcome that occurs is the result of an extended series of events and conditions, each stage of which is subject to substantial contingency and conjunctures. This is most visible in the occurrence of large, dramatic events like stock market crashes, peasant uprisings, and wars. But it is also true in more mundane occurrences — scandals, resignations, and insolvencies, for example.
The idea of path dependency is chiefly relevant in application to particular events and happenings. But there are large social structures that display path dependency as well. These examples amount to structuring conditions that persist for a long time and further condition other historical developments. Their emergence is contingent, and other directions were feasible in the early stage. But once the structure is in place it creates its own conditions for persistence. Because the Interstate highway program privileged automobile transport over rail in the 1950s, it is now difficult to create a financially viable passenger rail system in the United States.
Examples of historical developments that display significant path dependency include the choice of major technologies (internal combustion engines versus electric vehicles, alternating current rather than direct current as the long-distance power transmission standard, the QWERTY keyboard versus other more efficient arrangements), major infrastructures (rail rather than canal in the late nineteenth century, personal automobile rather than passenger rail in the mid-twentieth century), and the division of tasks and specialization across adjacent professions (social workers, psychiatrists). In each of these cases there is a contingent first step that could have led in another direction, and then an accumulated resistance to reverting to the other choice (substantial social investment already committed to the first option, substantial development of the knowledge systems required for the first option but not the second, substantial social power invested in individuals and organizations that have a vested interest in maintaining the first option, etc.). (Tom Hughes refers to these factors as “technological momentum” in Networks of Power: Electrification in Western Society, 1880-1930.) It isn’t impossible to retrace steps and adopt the alternative solution — but it is very difficult and uncommon.
James Mahoney has done useful work in explicating this concept in “Path dependence in historical sociology” (link). Here is how he describes his own position:
In this article, I argue that path dependence characterizes specifically those historical sequences in which contingent events set into motion institutional patterns or event chains that have deterministic properties. The identification of path dependence therefore involves both tracing a given outcome back to a particular set of historical events, and showing how these events are themselves contingent occurrences that cannot be explained on the basis of prior historical conditions. (507-508)
Mahoney identifies two basic mechanisms that are associated with path dependency:
First, some path-dependent investigators analyze self-reinforcing sequences characterized by the formation and long-term reproduction of a given institutional pattern. (508)
A second basic type of path-dependent analysis involves the study of reactive sequences. Reactive sequences are chains of temporally ordered and causally connected event. (509)
Here are the three features Mahoney finds to be critical.
I suggest that all path-dependent analyses minimally have three defining features. First, path-dependent analysis involves the study of causal processes that are highly sensitive to events that take place in the early stages of an overall historical sequence. (510)
Second, in a path-dependent sequence, early historical events are contingent occurrences that cannot be explained on the basis of prior events or “initial conditions.” (511)
Third, once contingent historical events take place, path-dependent sequences are marked by relatively deterministic causal patterns or what can be thought of as “inertia” – i.e., once processes are set into motion and begin tracking a particular outcome, these processes tend to stay in motion and continue to track this outcome. (511)
Mahoney’s work here represents a great example of careful, detailed analysis that crosses the categories of methodology, theory, and philosophy. This is how we make progress in the social sciences — by taking theories and concepts seriously and providing careful, logical analysis of the ways these concepts express important features of the historical process.
The idea of path dependency invokes the intersection of two important intuitions which are in tension with each other. The first is the sense of contingency that study of important historical transitions instills. The second is the idea that explanation involves generalizing across cases. If a case is wholly particular, then it is hard to find anything explanatory in studying it. Careful analysis of the concept of path dependency has the potential of offering a higher-level resolution of these intuitions about the historical process.