If scenarios are viewed as sequences, what does this mean? A sequence can consist of any kind of elements which somehow link to one another. In the following, I would like to specify the type of sequence that a scenario describes. I will argue that a scenario should be viewed as a narrative of a reactive sequence.
The concept of reactive sequences comes from the work of the sociologist James Mahoney. \citet{mahoney2000path} argues that there are two types of sequences that can be analysed using the framework of path dependence: self-reinforcing sequences and reactive sequences. Self-reinforcing sequences are perhaps the better known type, since the classic examples of path dependence, such as the QWERTY keyboard layout, represent this type of sequence. In a self-reinforcing sequence, an initial choice becomes entrenched over time due to increasing returns and other mechanisms of reproduction.
Some scenarios may be presented as self-reinforcing sequences, as kind of "winner takes all" narratives. However, I would argue that the second type of sequence, reactive sequence, is useful for futures research because it concerns change over time rather than persistence. \citet[][526]{mahoney2000path} gives the following definition of a reactive sequence:
Reactive sequences are chains of temporally ordered and causally connected events. In a reactive sequence, each event in the sequence is both a reaction to antecedent events and a cause of subsequent events.
The definition is simple but it has wide implications. Because early events constrain subsequent ones, their impact cascades throughout the entire sequence. This is similar notion to the notion in evolutionary futures studies that small fluctuations may ultimately have drastic impacts on outcomes \cite{Mannermaa_1991}. However, here the level abstraction is lower and the focus is on specific processes rather than attempting to explain overall societal development.
In reality, events are part of several sequences at the same time, and connecting them into coherent stories requires interpretation. Contemporary social scientists do not consider that there is a grand narrative such as progress or secularisation that encompasses all events and makes them understandable. Instead, narratives at different time horizons overlap and cross each other in complex ways. As \citet[][438]{Abbott_1992} states, "the full social process, when viewed in narrative terms, makes up a network of stories flowing into the present and future". Historical sociologists use the term conjuncture to represent the intersection of separate sequences \citep{mahoney2000path}. This concept is illustrated in Fig. 1, where S represents the conjuncture point which joins the two sequences beginning with A and M into a common sequence.