A delusion is a firm belief in something that is not true despite overwhelming evidence to the contrary.

According to The Diagnostic and Statistical Manual of Mental Health Disorders, Fifth Edition (DSM-V):

  • Delusions are fixed beliefs that are not amenable to change in light of conflicting evidence.
  • Their content may include a variety of themes (e.g. persecutory, referential, somatic, religious, grandiose).
  • Delusions are deemed bizarre if they are clearly implausible and not understandable to same-culture peers and do not derive from ordinary life experiences.
  • The distinction between a delusion and a strongly held idea is sometimes difficult to make and depends in part on the degree of conviction with which the belief is held despite clear or reasonable contradictory evidence regarding its veracity.
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