Can design faults be tolerated?

The fault tolerant approach to building reliable systems acknowledges that perfection is impossible (or at best very expensive) and therefore tries to cope with the consequences of residual defects within the system. Fault tolerance has an established role in detecting and masking component faults in hardware systems, but has also been advocated as a defence against deficiencies of design. The paper argues, in question and answer format, the case for adopting design fault tolerance techniques in practical systems.