A delusion is commonly defined as a
and is used in everyday language to describe a belief that is either false, fanciful or derived from deception.
the definition is necessarily more precise and implies that the belief is pathological (the result of an illness or illness
Delusions typically occur in the context of neurological or mental
illness, although they are not tied to any particular disease and have
been found to occur in the context of many pathological states (both physical
and mental). However, they are of particular diagnostic importance in psychotic
disorders and particularly in schizophrenia.
A false belief based on incorrect
inference about external reality that is firmly sustained despite what almost
everybody else believes and despite what constitutes incontrovertible and obvious
proof or evidence to the contrary. The belief is not one ordinarily accepted
by other members of the person's culture or subculture (e.g. it is not an
article of religious faith).
Primary and Secondary
Jaspers originally made a distinction between primary and secondary
According to Jaspers, primary delusions (sometimes called true delusions)
are distinguished by a transformation of meaning, so that the world, or aspects of it, are interpreted in a radically
different way by the delusional person. To others, this intepretation
is 'un-understandable' in terms of the normal mental causality, mood,
environmental influences and other psychological or psychopathological factors. Jaspers describes four
types of primary delusion:
intuition - where delusions arrive 'out of the blue', without
perception - where a normal percept is interpreted with delusional
meaning. For example, a person sees a red car and knows that this means
their food is being poisoned by the police.
atmosphere - where the world seems subtly altered, uncanny,
portentous or sinister. This resolves into a delusion, usually in a
revelatory fashion, which seems to explain the unusual feeling of
- where a delusional belief is based upon the recall of memory or false
memory for a past experience. For example, a man recalls seeing a woman
laughing at the bus stop several weeks ago and now realises
that this person was laughing because the man has animals living inside
Secondary delusions (sometimes called delusion-like ideas) are considered
to be, at least in principle, understandable in the context of a person's
life history, personality, mood state or presence of other psychopathology.
For example, a person becomes depressed, suffers very low mood and
self-esteem, and subsequently believes they are responsible for some terrible
crime which they did not commit.
However, the modern definition and Jaspers's
original criteria have been criticised, as
counter-examples can be shown for every defining feature.
Studies on psychiatric patients have shown that delusions can be seen to vary
in intensity and conviction over time which suggests that certainty and
incorrigibility are not necessary components of a delusional belief1.
Delusions do not necessarily have to be false or 'incorrect inferences
about external reality'2.
Some religious or spiritual beliefs (such as 'I believe in the existence of
God') including those diagnosed as delusional, by their nature may not be
falsifiable, and hence cannot be described as false or incorrect3.
In other situations the delusion may turn out to be true belief4.
For example, delusional jealousy, where a person believes
that their partner is being unfaithful (and may even follow them into the
bathroom believing them to be seeing their lover even during the briefest of
partings) may result in the faithful partner being driven to infidelity by
the constant and unreasonable strain put on them by their delusional spouse.
In this case the delusion does not cease to be a delusion because the content
later turns out to be true.
In other cases, the delusion may be assumed to be false by doctor or
psychiatrist assessing the belief, because it seems to be unlikely,
bizarre or held with excessive conviction. Psychiatrists rarely have the time
or resources to check the validity of a person’s claims leading to some true
beliefs to be erroneously classified as delusional5.
This is known as the Martha Mitchell effect, after the wife of
the attorney general who alleged that illegal activity was taking place in
the White House. At the time her claims were thought to be signs of mental
illness, and only after the Watergate scandal broke was she proved right
(and hence sane).
Similar factors have led to criticisms of Jaspers's
definition of true delusions as being ultimately 'un-understandable'. Critics
(such as R. D. Laing) have argued
that this leads to the diagnosis of delusions being based on the subjective
understanding of a particular psychiatrist, who may not have access to all
the information which might make a belief otherwise interpretable.
Another difficulty with the diagnosis of delusions is that almost all of
these features can be found in normal beliefs. Many religious beliefs hold
exactly the same features, yet are not considered delusional. Similarly, as Thomas Kuhn demonstrated in The Structure of Scientific
Revolutions (his groundbreaking book on the history and
scientists can hold strong fixed beliefs in scientific theories despite
considerable counter evidence for their validity6.
These factors have led the psychiatrist Anthony
David to note that "there is no acceptable (rather than accepted)
definition of a delusion"7.
In practice psychiatrists tend to diagnose a belief as delusional if it is
either patently bizarre, causing significant distress, or excessively
pre-occupies the patient, especially if the person is subsequently unswayed in their belief by counter-evidence or
V., Halligan, P.W. & Ellis, H. (2003)
Beliefs about delusions. The Psychologist, 16(8), 418-423. Full text (http://www.cf.ac.uk/psych/home/bellv1/pubs/BellHalliganEllis2003.txt)
M. & Davis, M. (2000) (Eds.) Pathologies of belief. Oxford:
R. (2003) From the Edge of the Couch: Bizarre Psychiatric Cases and
What They Teach Us About Ourselves. Bantam. ISBN
1Myin-Germeys, I., Nicolson, N.A. & Delespaul, P.A.E.G.
The context of delusional experiences in the daily life of patients with
schizophrenia. Psychological Medicine, 31, 489-498. 2Spitzer, M. (1990) (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2225797&dopt=Abstract)
On defining delusions. Comprehensive Psychiatry, 31 (5), 377-97 3Young, A.W. (2000).Wondrous strange: The neuropsychology
of abnormal beliefs. In M. Coltheart & M. Davis
(Eds.) Pathologies of belief (pp.47-74). Oxford:
0631221360 4Jones, E. (1999) (http://muse.jhu.edu/journals/philosophy_psychiatry_and_psychology/toc/ppp6.1.html)
The phenomenology of abnormal belief. Philosophy, Psychiatry and
Psychology, 6, 1-16. 5Maher, B.A. (1988) Anomalous experience and delusional thinking:
The logic of explanations. In T. Oltmanns and B.
Maher (eds) Delusional Beliefs. New
York: Wiley Interscience.
0471836354 6Kuhn, T. (1962) The Structure of Scientific
Revolutions. University of Chicago
0226458083 7David, A.S. (1999) On the impossibility of defining delusions. Philosophy,
Psychiatry and Psychology, 6 (1), 17-20