In essence, the mental model theory "won" the debate, but this was mostly a hollow victory, as both theories have become largely irrelevant.
For in-depth reviews, see for example: Holyoak & Morrison (2012), Oaksford & Chater (2007), Ball & Thompson (2017), Over (2020). To summarize however, a few factors have led to this outcome:
- The mental models theory has been refined over the years, whereas mental logic (aka mental rules or formal rule approach) has fallen out of favour - eg, López-Astorga (2016), Evans (2012):
Within the psychology of reasoning, the view that there is an in-built
mental logic in the form of inference rules is nowadays a minority
position, and even these theorists propose substantial variation from
standard logics as well as a host of performance factors.
- Much of the debate became immaterial when researchers attempted to extend these 2 models to logical reasoning and critical thinking more generally - eg, Evans (2012):
... experimental evidence has accumulated indicating that people were
apparently poor at logical reasoning, highly influenced by irrelevant
features of the content and subject to a number of other cognitive
biases. As a result, the paradigm has shifted in the past 10-15
years, and while deduction is still studied, it is allied to a number
of other methods. Theoretically, there is now also a lot more interest
in human reasoning as a probabilistic and pragmatic, rather than
deductive process.
- This eventually lead to the popularity of much more comprehensive, and empirically successful, dual-process and (Bayesian) probabilistic theories, that subsume the mental logic and model theories, and created what is now known as the "new paradigm psychology of reasoning", integrating the psychology of reasoning with the study of judgement and decision-making.
Bonnefon (2013):
During the late 1990s and the early twenty-first century, the
psychology of reasoning slowly moved towards a broader range of
problems than deduction, ... which eventually coalesced into what some
call the New Paradigm psychology of reasoning. ... It became
increasingly common for psychologists to observe that people did very
little deducing in everyday life, and that the study of deduction was
accordingly unlikely to deliver general insights about how people
reasoned.
Elqayam & Over (2012):
A Bayesian approach is indisputably a core element of this new
paradigm—any approach within this paradigm takes into account degrees
of belief and uncertainty. In this paper, we argued that dual
processing is just as much a part of the new paradigm. ...
Bayesianism, in turn, constrains the way dual processing is theorised,
precluding the older mental logic or mental models interpretation.
Oaksford & Chater (2019):
The two most prominent old-paradigm theories make different
assumptions about mental representations and processes. Mental logic
proposes that the mind mirrors syntactic representations and the
application of logical rules, as above. By contrast, mental models
theory (MMT) assumes that people reason over representations that
attempt to capture what the premises mean. ... The new paradigm in the
psychology of reasoning, by contrast, attempts to explain
argumentation, deduction, and induction in a probabilistic framework,
in continuity with models that have become widespread in the cognitive
and brain sciences.