Every liability insurance policy has to answer a threshold question before coverage analysis can even begin: which policy, out of however many the insured purchased over the years, applies to this claim? The answer depends on the policy's trigger. An occurrence policy is triggered by the injury or damage itself happening during the policy period, regardless of when the claim is later made. A claims-made policy is triggered by the claim being made against the insured (and often reported to the insurer) during the policy period, regardless of when the underlying injury occurred.

The distinction matters most for latent or progressive harm: environmental contamination, asbestos exposure, product defects that manifest years later, and professional malpractice discovered long after the negligent act. In those cases the choice of trigger theory can determine which of a decade's worth of policies, if any, must respond.

An occurrence policy generally covers injury or damage that takes place during the policy period, even if the claim is not made until years afterward, so long as the policy was in force when the underlying event occurred. This makes occurrence coverage 'tail-proof' from the insured's perspective: once a policy year is triggered, that policy typically remains available to respond to a claim asserted long after the policy has expired, subject to the terms in force at the time.

A claims-made policy instead covers claims first made against the insured during the policy period (or during an extended reporting period purchased or provided under the policy), regardless of when the underlying conduct occurred, so long as the conduct is not otherwise excluded, such as by a retroactive date. Because coverage depends on when the claim surfaces and is reported rather than when the underlying act happened, claims-made insureds who switch carriers or let a policy lapse can find themselves with a coverage gap for conduct that occurred while insured but is not claimed until after the switch, unless tail coverage is purchased.

Where injury develops gradually, occurring across multiple policy periods (progressive property damage, disease from repeated exposure), courts have adopted competing trigger theories: an exposure theory (coverage attaches in every period exposure occurred), a manifestation theory (coverage attaches only in the period the injury became diagnosable or apparent), an injury-in-fact theory (coverage attaches in the period actual biological or physical injury occurred, as later determined by expert evidence), and a continuous trigger theory (every policy in force from first exposure through manifestation is triggered). Which theory a jurisdiction follows can multiply, or eliminate, the number of policies available to respond to a single claim.

Juricratic models the trigger question as an upstream gate that determines which downstream duty-to-defend and duty-to-indemnify paths are even in play. For a progressive-harm fact pattern, a user can set the trigger-theory dial across exposure, manifestation, injury-in-fact, and continuous-trigger positions and see, as a simulation artifact rather than a legal conclusion, how the set of implicated policy periods and insurers expands or contracts under each assumption.