The following indicate a delusion:
1. The person expresses an idea or belief with unusual persistence or force.
2. That idea appears to exert an undue influence on his or her life, and the way of life is often altered to an inexplicable extent.
3. The individual tends to be humorless and oversensitive, especially about the belief.
4. An attempt to contradict the belief is likely to arouse an inappropriately strong emotional reaction, often with irritability and hostility.
5. The person is emotionally over-invested in the idea and it overwhelms other elements of his or her reasoning.
The following features are found:
1. It is a stable disorder characterized by the presence of delusions to which the person clings with extraordinary tenacity.
2. The condition is chronic and frequently lifelong.
3. The delusions are logically constructed and internally consistent.
4. The delusions do not interfere with general logical reasoning (although within the delusional system the logic is perverted) and there is usually no general disturbance of behavior.
5. The individual experiences a heightened sense of self-reference. Events which, to others, are nonsignificant are of enormous significance to him or her, and the atmosphere surrounding the delusions is highly charged.
6. For the deluded, their own beliefs are single-mindedly asserted and imposed as an objective reality for all others.