Abstract
In insurance, terms and conditions by insurers at the end of proposal forms or insurance contracts will be included in print that the insured has confirmed the authenticity of answer to questions and provided information, and agrees that the statements are "basis of contract". If an inaccuracy of those announcements proves later, insurer regardless of the importance of statements in acceptance of the risk or determination of the premium can disclaim based on this clause himself and avoid the contract. The basis of condition clause is emerged from common law and also used in insurance law of Iran. This condition in that system after decades that has been criticized faced with notable changes. In this article, the issue, nature and consequences of the basis of contract clause is studied, not to use such expressions and conditions in proposal forms but insurance contract is suggested since it leads to injustice against the insured.