Illinois is a “four corners” state that holds that interpretation of an insurance policy to determine a duty to defend relies totally upon the wording of the lawsuit and the policy. No facts extrinsic to the pleadings or the policy wording are allowed to impinge upon the court's analysis of the duty to defend. This rule, followed in several but by no means a majority of states, often results in rulings that put defendants and their insurers at the mercy of the plaintiff pleading a lawsuit against the defendant.

For example, if a party plaintiff wishes to punish the defendant, it can instruct its lawyers to plead the lawsuit in terms of intentional tort—assault, battery, trespass, etc.— rather than negligence. Thus, reviewing the four corners of the lawsuit and the four corners of the policy, the insured can never receive defense from its insurer whose policy would necessarily not include coverage for intentional acts.

Similarly, a prudent plaintiffs' lawyer whose client was injured by an intentional tort like battery will plead a suit against the aggressor in terms of negligence so that the aggressor's insurer will defend and eventually indemnify the aggressor.