Why do humans reason? Arguments
for an  argumentative theory

Hugo Mercier
Philosophy, Politics and Economics Program, University of  Pennsylvania,
Philadelphia, PA 19104
[email protected]_ (mailto:[email protected])  
_http://sites.google.com/site/hugomercier/_ 
(http://sites.google.com/site/hugomercier/) 

Dan Sperber
Jean Nicod Institute (EHESS-ENS-CNRS), 75005 Paris,  France; Department
of Philosophy, Central European University, Budapest,  Hungary
[email protected]_ (mailto:[email protected])  _http://www.dan.sperber.fr_ 
(http://www.dan.sperber.fr) 

Abstract :  Reasoning is  generally seen as a means to improve knowledge 
and make better decisions.  However, much evidence shows that reasoning often 
leads to epistemic distortions  and poor decisions. This suggests that the 
function of reasoning should be  rethought.

Our hypothesis is that the function of reasoning is argumentative. It  is 
to devise and evaluate arguments
intended to persuade. Reasoning so conceived is adaptive given the  
exceptional dependence of humans on communication and their vulnerability to  
misinformation. A wide range of evidence in the psychology of reasoning and  
decision making can be reinterpreted and better explained in the light of this  
hypothesis. Poor performance in standard reasoning tasks is explained by the 
 lack of argumentative context. When the same problems are placed in a 
proper  argumentative setting, people turn out to be skilled arguers. 
 
Skilled arguers, however, are not after the truth but after arguments  
supporting their views. This explains the notorious confirmation bias. This 
bias 
 is apparent not only when people are actually arguing, but also when they 
are  reasoning proactively from the perspective of having to defend their 
opinions.  Reasoning so motivated can distort evaluations and attitudes and 
allow erroneous  beliefs to persist. Proactively used reasoning also favors 
decisions that are  easy to justify but not necessarily better. In all these 
instances traditionally  described as failures or flaws, reasoning does 
exactly what can be expected of  an argumentative device: Look for arguments 
that 
support a given conclusion,  and, ceteris paribus, favor conclusions for 
which arguments can be found.

Keywords: argumentation; confirmation bias; decision making; dual  process 
theory; evolutionary psychology; motivated reasoning; reason-based  choice; 
reasoning
 
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