Dual systems theory: in what sense are the systems 'unreal'? In the course of explain dual systems theory, Kahneman (2011) discusses the Heider study, in which: 


  you see a large triangle, a small triangle, and a circle moving around
  a shape that looks like a schematic view of a house with an open door.
  Viewers see an aggressive large triangle bullying a smaller triangle,
  a terrified circle, the circle and the small triangle joining forces
  to defeat the bully.


Viewers perceive the movements of the shapes in causal terms. Kahneman then goes on to say:


  The psychology of causality was the basis of my decision to describe
  psychological processes by metaphors of agency, with little concern
  for consistency. I sometimes refer to System 1 as an agent with
  certain traits and preferences, and sometimes as an associative
  machine that represents reality by a complex pattern of links. The
  system and the machine are fictions; my reason for using them is that
  they fit the way we think about causes. Heider’s triangles and circles
  are not really agents—it is just very easy and natural to think of
  them that way. It is a matter of mental economy. I assume that you
  (like me) find it easier to think about the mind if we describe what
  happens in terms of traits and intentions (the two systems) and
  sometimes in terms of mechanical regularities (the associative
  machine). I do not intend to convince you that the systems are real,
  any more than Heider intended you to believe that the large triangle
  is really a bully.


I've never been able to understand the distinction he is trying to draw there. In what sense are the two systems 'unreal'?

Kahneman, D. (2011). Thinking, fast and slow. Macmillan.
What Kahneman means is that these are nothing but comparisons, or metaphors, to indirectly explain cognitive processing. Neither you nor I have physically seen these two systems exist, BUT the existence of such systems may be implicated through neural representations. Kahneman has used economic metaphors (concept of resources and their allocation) in his capacity model of attention (1973). (1)

The following excerpt from John B. Best's Cognitive Psychology, fifth edition (2) , might help. Here, he talks about the rationale behind using a metaphor (the information-processing or computer metaphor) in cognitive psychology:


  Because the information-processing viewpoint is necessarily abstract, why use it to study cognitive processes, especially when it might be possible to study the underlying neural processes directly? In other words, the students seem to suggest that we simply cut to the chase and study neural processes themselves. What stops us? Information-processing theories might argue that an abstract analysis is necessary because of discoverability problems at the neural level. It's true that specific relationships may always be discoverable between specific neural activities or locations, and particular cognitive or mental events... Despite this reservation, however, cognitive psychologists working in the information-processing tradition maintain that there are no guarantees that a general, discoverable neural representation inevitably underlies all specific cognitive events."


TL;DR: It's a metaphor, an indirect comparison to how cognitive processes occur, for ease of understanding.



1) There has been considerable debate regarding whether the concept of using strict, dichotomous systems is a good way to represent cognitive processing and why and how dual-process theories like Kahneman's fail in some aspects. Highly recommend reading some of the highlighted points in The Mythical Number Two by Melnikoff and Bargh (2018), published in Trends in Cognitive Sciences.

2) An edition of the book is available to borrow on archive.org and you may find this quoted text in the first introductory chapter.