Objective: There are two general theoretical explanations for delusions, the deficit and the motivational. In the deficit approach, scientists have argued that delusions are the consequences of fundamental perceptual or reasoning deficits which cause the individual to misunderstand what is happening in the world. The second approach views delusions as serving a defensive, palliative function, as representing an attempt to relieve pain, tension and distress. Methods: The present review article is based on literature review about Paranoid Delusion theories. Results and Conclusion: This article reviews the most important theories in the above mentioned approaches and it has found that we need more studies to verify the results of these approaches. The deficits in reasoning ability for example, need more explanations to show how and why these deficits occur and cause persecutory delusions. In this article I suggest that there are basic cognitive impairments that lead to disturbances in the mental imagination. These disturbances result on the two cognitive deficits (two losses) and force a person to have delusional beliefs. This study is a qualitative study based on judgments of some cases which the researcher has had the opportunity to study