The phenomenon of post-truth, in which truth (or facts or the best scientific
evidence) is brushed aside in public debates, has recently caught the eye of
many philosophers, who typically see it as a threat to deliberative
democracy. In this paper, it is argued that Gustave Le Bon?s remarks on
crowd psychology, which had been very popular in past (and brushed aside
later on), might be relevant for a better understanding of psychological
mechanisms that lead to post-truth. According to Le Bon, crowds are often
irrational, whereas those who try to convince them to do something should
use specific techniques of persuasion, such as affirmation, repetition,
contagion and prestige, of which the last one can be undermined either by
fiasco (the fastest way), or by critique (a bit slower, but nonetheless
effective way). It is the age of posttruth that goes towards the
neutralization of any critique (Le Bon himself considered such
neutralization devastating for democratic societies), which has been,
according to some authors, affected to a great extent by technological
innovations in media, such as social media that some authors consider
anti-social due to their negative impact on society. I argue that Le Bon?s
insights might be useful to members of scientific and philosophical
community in their attempts to eliminate the spreading of quasi-scientific
views in public discourse.