The number of accidents which are caused by the existence of defects in engineering structures can be reduced in two ways,

1. By diminishing the number and size of the defects, either by making the structure more carefully in the first place or by using better inspection methods in service - or by some combination of the two.
2. By designing structures which are inherently safer - that is to say less susceptible to the presence of defects. An 'ideal' structure could be shot full of holes and still not break.

In fact there will always be some defects in every structure for no manufacturing process and no inspection procedure can be perfect. Furthermore defects will accumulate in a structure between inspections due to fatigue, corrosion, accidental impacts, bad servicing, enemy action and so on. This paper is therefore about the philosophy of the imperfect structure. Since Nature has to deal with similar problems - because no plant or animal is perfect - I am making no apology for using analogiffi and examples from the new and expanding and exr.iting discipline of biomechanics. That is to say from the science of the mechanical strength of living structures.