Insurance practitioners in Texas are familiar with the so-called “eight corners rule” applied by Texas Courts to determine whether an insurer has a duty to defend a suit against its insured. The “eight corners rule” is simply summarized:
Under the eight-corners rule, the duty to defend is determined by the claims alleged in the petition and the coverage provided in the policy. The rule takes its name from the fact that only two documents are ordinarily relevant to the determination of the duty to defend: the policy and the pleadings of the third-party claimant. Facts outside the pleadings, even those easily ascertained, are ordinarily not material to the determination and allegations against the insured are liberally construed in favor of coverage.