Classically, the introduction of new technologies is often described as following an S-curve that assumes uptake is initially slow in the earliest stages prior to a dominant design emerging, until performance and functional benefits of the new technology are seen to be greater than those of existing technologies, at which point uptake significantly accelerates \cite{richard1986innovation,utterback1994mastering}. This model assumes that eventually all technologies then arrive at a limiting condition where they too begin to stagnate as uptake reduces (potentially due to market saturation or competition from new technologies), with substitution to a subsequent generation of technologies occurring either before or after arriving at this temporary plateau (see Fig. \ref{402288}). This brings about the notion of continual technological (or functional) failure, at the point where a replacement technology is sought for the current technological paradigm. However, the technological 'failures' that lead to this type of substitution vary greatly, and cannot just assume a single simple definition. In this regard, previous work has examined what is meant by 'technological failure', and has broadly categorised these occurrences into three main definitions \cite{Gooday_1998}:
- ‘Failure’ as a social taxonomy of marginalised technologies: ‘Failure' is not an essential characteristic of the technology itself. Instead 'failure' depends on a diverse range of usage factors that may not be replicated in other cultures, and is chronologically bounded so that any given technology can be classed as a success or failure at a given point in time according to social responses to it. This definition implies that ‘failure' is a completely unexceptional matter in technology, and that all 'successful' technologies 'fail' at some point in their existence \cite{Gooday_1998}
- ‘Failure’ as a mundane feature of technological usage and development: Persistent 'failure' of technology is an unavoidable consequence of ever more demanding expectations that human users impose upon their all-too-limited constructions. As such, what 'fails' is human expectations of hardware performance and distribution - or rather a 'failure' of socio-technical relations \cite{pye1978nature,Gooday_1998}
- 'Failure' as a perspectival and often contested attribution: many recent sociological studies of technology employ two simplifying assumptions; firstly that there is a decisive closure point in history at which a technology is judged a 'success' or a 'failure', and secondly that at this point in time, all parties come to a decision that is ultimately consensual, despite being based on differing perceptions of the technology's social role. Both of these assumptions can be challenged by strong counter-arguments \cite{Gooday_1998}
In the analysis that follows, this study focuses on the first of these three conditions (whilst the other two are addressed to a greater extent in separate technology adoption modelling work). Specifically, the definition of technological failure used in this study is given as:
“A point in time at which technology performance development stagnates/plateaus, with no further progressive trajectory improvements foreseen for a significant period of time in comparison to the overall technology lifecycle considered, which is subsequently followed by the substitution of a new technology/architecture that is on a progressive trajectory”
This means that a technology has been able to reach what could be observed to be a temporary performance limit in this condition before substitution to a new discontinuous technology occurs \cite{Schilling_2009}. This definition also follows on from the work of Sood & Tellis which applied a sub-sampling approach to analyse different types of 'multiple S-curves', and subsequently concluded that technologies tend to follow more of a step-function, with long periods of static performance interspersed with abrupt jumps in performance, rather than a classical S shape. In this study, stagnation periods were recorded where technology performance during a given sub-sample had an upper plateau longer in duration than the immediately preceding growth phase, whilst the subsequent jump in performance in the year immediately after the plateau was almost double the performance during the entire plateau \cite{Sood_2005}. Other studies, including the work of Chang and Schilling, classify multiple S-curves based on whether successive curves intersect or are disconnected \cite{Chang_2010,Schilling_2009}.
Anomalies associated with scientific and technological crisis
Up till now, only substitution patterns associated with technological failure have been discussed. However, previous studies have identified that technological substitutions are not just the result of the existing technology being deemed to have 'failed'. In this sense Edward Constant argued that a feature common to all technological revolutions was the emergence of 'technological anomalies', which could be traced to either scientific or technological crisis. The first, and most common cause of these technological anomalies results from functional failure, where:
"either the conventional paradigm proves inappropriate to "new or more stringent conditions", or an individual intuitively assumes that (s)he can produce a better or a new technological device" \cite{II_1973}
Alternatively, technological anomalies can arise as a result of presumptive technological leaps:
"The demarcation between functional-failure anomaly and presumptive anomaly is that presumptive anomaly is deduced from science before a new paradigm is formulated and that scientific deduction is the sole reason for the sole guide to new paradigm creation. No functional failure exists; an anomaly is presumed to exist, hence presumptive anomaly" \cite{II_1973}
Whilst technological revolutions may originate from either scientific or technological crisis, a critical area of commonality lies in the anomaly-crisis process observed in both conditions:
"in both science and technology anomaly causes certain individuals to reject the conventional paradigm and to create new paradigms, and, in each, crisis may lead to revolution" \cite{II_1973}
The type of crisis that emerges is dependent on which type of anomaly precedes it. Scientific crisis can occur irrespective of whether an alternative theoretical framework exists or not when a persistent, unresolved, scientific anomaly successfully refutes an established theory. In this condition the crisis is directly linked to the anomaly. However, technological anomaly and crisis are rarely so logically driven, and can arise in conditions where existing technological paradigms are still performing favourably. This is illustrated by the turbojet revolution of the 1930s and 1940s where piston-engine developments had provided remarkable performance improvements and continuing success, but were superseded by scientific advances that were directly responsible for the radical technological changes that followed. In addition, in order for a technological anomaly to provoke a technological crisis, a convincing alternative paradigm must exist, so that the relative functional failure of the conventional system is observable. As such, the alternative technological paradigm instigates the crisis, whilst the technological anomaly may only be seen as speculation or as a limiting condition to the normal technology \cite{II_1973}.
Modes of substitution
Based on the definitions of functional failure and presumptive anomaly described in sections \ref{677399} and \ref{646617}, this study examines the ability to distinguish between these two modes of substitution (i.e. reactive or presumptive) from analysis of historical scientific and technological data. Table \ref{table:technology_categories} uses these definitions and performance evidence obtained from literature to classify a sample set of technologies according to the mode of substitution observed.