Prevention Principle

An architect responsible for the administration of a construction contract should be aware of a legal concept enforced by the Courts called the 'Prevention Principle'. 

The principle is that when a time is specified for completion of a contract, so that the time is 'of the essence', an act by one party (the client) which prevents the other (the contractor) from completing the work on time, will put the time for completion 'at large'.  The principle is that the party preventing the other from completing on time cannot have the benefit of enforcing a contractual obligation - specifically, completion by a certain date.