In This Issue
Winter Issue of The Bridge on Complex Unifiable Systems
December 15, 2020 Volume 50 Issue 4
The articles in this issue are a first step toward exploring the notion of unifiability, not merely as an engineering ethos but also as a broader cultural responsibility.

Unity of Engineering Disciplines

Thursday, December 17, 2020

Author: Zachary Pirtle

To help engineers exploring how best to unify complex systems, I offer observations from the history of the philosophy of science, focusing on unity (and disunity) among engineering and scientific disciplines. Unity involves the extent to which different disciplines share common features, but this can still mean many things, and different disciplines approach problems in seemingly discordant ways. I draw on the work of logical empiricists to explore how disciplines vary in their language and methods as well as in their scientific laws, theories, and causal explanations.

Why Does (Dis)Unity Matter to Engineers?

Most engineers recognize that different disciplines can be incongruous: some disciplinary confusion is a part of any major systems development.

Consider airplanes. Engineers specializing in thermal, stress, electrical, propulsion, and aerodynamics disciplines will all see an airplane system differently, and focus only on their subset of the system. For example, stress engineers see the loads on the plane and the vibration frequencies caused by flight, and their design goals may want materials that are high strength to stiffen the plane and survive loads during operations. But the heavier mass of those materials might make the job of the aerodynamicist harder, as she seeks to protect speed and to design an efficient profile of the plane.

Managers and systems engineers interacting with discipline experts have to tie everything together, balancing the competing needs of individual disciplines. Many engineering systems today are more complex than airplane design, especially when interwoven with society and a broad array of actors. In combining engineering disciplines with physical and social sciences, the variety of intellectual disciplines requires some art in bringing them together usefully to solve a problem.

To explore what unity is, I discuss a vignette from the long history of interdisciplinary philosophy. Beginning in the 1930s, the logical empiricists Rudolf Carnap and Otto Neurath led a movement studying the unity of science. They both sought to define its nature and to create bridges across disciplines.

Starting in 1934 Neurath and others convened six International Congresses for the Unity of Science, bringing together physicists, psychologists, philosophers, economists, and others. Through the Institute for the Unity of Science, established 2 years later, Neurath and others solicited monographs from experts who described their disciplines in an encyclopedic way that would be accessible to those outside their field of expertise. These monographs eventually included Thomas Kuhn’s Structure of Scientific Revolutions (1962), which established much of modern thinking about paradigm change and revolution.

Dimensions of (Dis)Unity

What are the key dimensions of (dis)unity across scientific disciplines, and how unified are the sciences? I will briefly illustrate this by building on some of Carnap’s (1938) terms.

Unity of Language and Method

Carnap first decomposed the question of unity by asking if the language of science was unified across disciplines. While most disciplines use terms that vary significantly, they all describe features that are eventually observable in the physical world and make claims that should be publicly testable through observation.

Unity of language might additionally be interpreted to reflect questions about the differing methods of scientific disciplines and to what extent practitioners create knowledge differently, making unique inferences based on the language they use. The above airplane example helps illustrate the divergent terms and methods that engineers in different areas of expertise may use to analyze the same system.

Unity of Laws and Theory

Carnap asked whether there is a unity of scientific law across disciplines. We might view unity of law here more broadly, considering whether the collected scientific theories underlying a given discipline are compatible and unifiable with one another.

Breakthroughs in general relativity were changing the nature of laws in physics in Carnap’s time, raising questions about getting to a unified set of laws of physics and whether those laws could inform progress in chemistry, biology, and other fields. Unity of theory was not taken for granted among the logical empiricists, and Carnap viewed the extent to which theory across different disciplines like biology and physics could be unified as an empirical question, where actual success in combining theories and laws would trump any armchair philosophizing.

Engineers might care a lot about the extent to which their theory is unifiable, if not derived, from physics and other fields. Walter Vincenti (1990) showed that many engineers create knowledge that is distinct from science, and suggests the importance of dedicated support for engineering knowledge independent of applied science.

Recognizing Plurality in Complex Systems

Today, both scholars and practitioners more frequently recognize the disunity of science, in their use of varying language, methods, laws, and theory. Most philosophers of science, like Stéphanie Ruphy (2016), speak of the “plurality of science” to recognize the ways scientific disciplines are unique, and she encourages detailed study of varied scientific practices.

While many see some commonality in the funda-mental language of science, philosophers like Ruphy and Nancy Cartwright (1999) argue that it is not possible to unify laws and theory across disciplines. Practicing engineers may believe in the eventual possibility of unifying theory across disciplines, but they likely sympathize with the incongruous disciplinary perspectives that I noted above, and may wonder about a disunity of theory.

However, the need to take action to shape complex systems does not let us rest easily with accepting the disunity of science. If a multidisciplinary team of experts seek to explain why a system problem occurs and how to resolve it, it matters if they see the same causal mechanisms underlying the problem. Recognizing that differing experts have different theories on what causes change in a system is important, and should lead teams to recognize uncertainty around individual expert recommendations.


Deeper reflection could proceed on two main paths: as engineers and scientists, we can either accept disunity across disciplines and study how to usefully combine a plurality of independent disciplines to guide action. Or we can try to clarify the conceptual underpinnings across disciplines, to create unity by conceptually engineering shared theoretical understandings and methods, for particular problems if not in general.

The work of Carnap and Neurath serves as a -reminder of how complex the concept of unity can be, and as a great programmatic example for how engineers can have an inclusive, accessible, and proactive movement to bridge gaps across engineering and scientific disciplines.


Carnap R. 1938. Logical foundations of the unity of science. In: International Encyclopedia of Unified Science, Vol 1, eds Neurath O, Carnap R, Morris CW. University of -Chicago Press.

Cartwright N. 1999. The Dappled World: A Study of the Boundaries of Science. Cambridge: Cambridge University Press.

Kuhn T. 1962. Structure of Scientific Revolutions. University of Chicago Press.

Ruphy S. 2016. Scientific Pluralism Reconsidered: A New Approach to the (Dis)Unity of Science. University of Pittsburgh Press.

Vincenti W. 1990. What Engineers Know and How They Know It: Analytical Studies from Aeronautical History. Baltimore: Johns Hopkins University Press.

About the Author:Zachary Pirtle is an engineer and has served as cochair of the Forum on Philosophy, Engineering, and Technology.