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The Core Idea

According to a (modest) dual process theory, there are two (or more) mindreading processes which are distinct in this sense: the conditions which influence whether they occur, and which outputs they generate, do not completely overlap.

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What Is a Two-Systems Theory? The Core Idea

In general, a modest two-systems theory concerning some cognitive domain (e.g. numerical cognition or moral cognition) claims just this:

Two (or more) processes which enable functioning in this domain are distinct: the conditions which influence whether they occur, and which outputs they generate, do not completely overlap.1

One process is faster than another: it makes fewer demands on scarce cognitive resources such as attention, inhibitory control and working memory.

A key feature of this two systems theory is its theoretical modesty: it involves no a priori commitments concerning the particular characteristics of the processes. Identifying characteristics of the process is a matter of discovery.

Further, their characteristics may vary across domains. The characteristics that distinguish processes involved in mindreading may not entirely overlap with those that distinguish processes involved in physical cognition, or in numerical cognition, or in moral cognition.

Minimal Illustration: Toxicity

What do you compute that enables you to track toxicity?

Option 2 (slow but accurate): measure molecular composition (feed it to shellfish and use liquid chromatography-mass spectrometry).

Option 1 (limited but fast): experience disgust …

‘Disgust is thought to have originated in distaste, a food-rejection impulse or motivation triggered by the ingestion of unpleasant-tasting substances, prototypically those that are bitter (Chapman, Kim, Susskind, & Anderson, 2009; Rozin & Fallon, 1987). Because many bitter substances are toxic (Garcia, Hankins, Denton, & Coghlan, 1975), the role of distaste in food rejection has a clear and concrete adaptive function. Distaste appears to have very ancient origins: Even sea anemones, which first evolved some 500 million years ago, will expel bitter foods from their gastric cavity (Garcia et al., 1975)’ (Chapman & Anderson, 2013, p. 300).

In Which Domains Are There Two-Systems Theories?

Two-systems theories of one kind or another have been proposed for various domains. Here is a partial list of domains (note that some domains may overlap):

There are also domains where it is arguably coherent to suppose that researchers have identified what might be called a two-systems theory although this terminology is not in common use:

Systems 1 and 2 ???

Two systems theories often make claims beyond the core idea:

‘Typically, one of the processes is characterized as fast, effortless, automatic, nonconscious, inflexible, heavily contextualized, and undemanding of working memory, and the other as slow, effortful, controlled, conscious, flexible, decontextualized, and demanding of working memory’ (Frankish & Evans, 2009, p. 1).

As several researchers have pointed out, this way of characterising systems goes beyond the evidence available and depends on assumptions about the characteristics coming in neat bundles (Adolphs, 2010; Keren & Schul, 2009).

There may also be reasons to doubt that bold hypotheses about these characteristics do much, if any, explanatory work (Butterfill, 2007; Butterfill, 2020).4

Dual-Process or Two-Systems?

Although two systems theories are sometimes understood as making claims over and above those of a dual-process theory (e.g. Gawronski et al., 2014), others do not make any distinction:

‘We use the term “system” only as a label for collections of cognitive processes that can be distinguished by their speed, their controllability, and the contents on which they operate’ (Kahneman & Frederick, 2005, p. 267).

We shall follow Kahneman in treating ‘Two-Systems’ and ‘Dual-Process’ as synonyms unless we encounter a need to distinguish them.


automatic : On this course, a process is _automatic_ just if whether or not it occurs is to a significant extent independent of your current task, motivations and intentions. To say that _mindreading is automatic_ is to say that it involves only automatic processes. The term `automatic' has been used in a variety of ways by other authors: see Moors (2014, p. 22) for a one-page overview, Moors & De Houwer (2006) for a detailed theoretical review, or Bargh (1992) for a classic and very readable introduction
cognitively efficient : A process is cognitively efficient to the degree that it does not consume working memory and other scarce cognitive resources.
fast : A fast process is one that is to to some interesting degree cognitively efficient (and therefore likely also some interesting degree automatic). These processes are also sometimes characterised as able to yield rapid responses.
Since automaticity and cognitive efficiency are matters of degree, it is only strictly correct to identify some processes as faster than others.
The fast-slow distinction has been variously characterised in ways that do not entirely overlap (even individual author have offered differing characterisations at different times; e.g. Kahneman, 2013; Morewedge & Kahneman, 2010; Kahneman & Klein, 2009; Kahneman, 2002): as its advocates stress, it is a rough-and-ready tool rather than an element in a rigorous theory.
tracking an attribute : For a process to track an attribute is for the presence or absence of the attribute to make a difference to how the process unfolds, where this is not an accident. (And for a system or device to track an attribute is for some process in that system or device to track it.)
Tracking an attribute is contrasted with computing it. Unlike tracking, computing typically requires that the attribute be represented.


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Apperly, I. A., & Butterfill, S. (2009). Do humans have two systems to track beliefs and belief-like states? Psychological Review, 116(4), 953–970.
Bargh, J. A. (1992). The Ecology of Automaticity: Toward Establishing the Conditions Needed to Produce Automatic Processing Effects. The American Journal of Psychology, 105(2), 181–199.
Bicchieri, C. (2016). Norms in the wild: How to diagnose, measure, and change social norms. Oxford: Oxford University Press.
Butterfill, S. A. (2007). What are modules and what is their role in development? Mind and Language, 22(4), 450–473.
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  1. Compare Frankish & Evans (2009, p. 1): ‘These theories come in different forms, but all agree in positing two distinct processing mechanisms for a given task, which employ different procedures and may yield different, and sometimes conflicting, results.’ 

  2. We have linked the sources to references chosen to be accessible and useful; these are not the first or canonical sources for two-systems theories. 

  3. Note that the balance of evidence may not currently support the Gilbert et al. (2006)’s findings (see Witzel & Gegenfurtner, 2011). 

  4. The bold hypotheses do, however, make dual-process theories readily falsifiable. As Gawronski et al. (2014, p. 11) note, ‘the number of events prohibited by dual-process theories—and thus their falsifiability—increases with the number of proposed covariations between dualities.’ As we will see in considering mindreading and physical cognition, there are other ways to ensure that a dual-process theory is readily falsifiable.