Delusions are defined as a) false beliefs, b) that are held with extraordinary conviction and incomparable subjective certainty, c) that are impervious to to other experiences and to compelling counterargument, and d) their content is impossible. They are also defined as out of keeping with the person's educational and social background.

There is little doubt that this definition is not without criticism. Is the falsity of delusions necessary to the definition? Is conviction an important feature of delusions? Need delusions be out of keeping with educational and social background? A number of authors define delusions as products of irrational thinking or of incorrect inference? Is this necessarily the case?

The aim of this talk is to address these and other questions. I will argue that the term ‘delusion’ is merely a descriptive term similar to a term such as ‘abnormal movement’. This means that a number of phenomena that have a superficial family resemblance are grouped together and discussed as if they were the same phenomenon. This approach would be similar to tremors, athetosis, ballistic movements, and akinesia all being grouped together as the same phenomenon. Furthermore, I will argue that there are different kinds of delusions and I do not mean by this the usual classification into primary and secondary delusions or of classification of delusions by their content.

Finally, I will argue that there are beliefs about the world that are at the cornerstone of how the material world operates and that it is deviations from these jointly held communal beliefs that structure how human beings experience the world that determine what is a delusion. In other words that it is not conviction, or irrationality, or for that matter deviation from social and educational background that determine what delusions are.

Rather something anomalous about how the world is described and experienced by the person with delusions.

The talk will conclude by suggesting a radical revision of our approach and understanding of the nature of ‘delusions’.