Behe's name for the idea of a system which would stop working if any of its components was removed. Such systems evolve quite often.

The concept that systems contain components which by themselves hold no value until they are brought together into a working system. Michael Behe is a major proponent of this thinking. The common example he uses is the mouse trap which has many parts which have no individual value until they are put together as a mouse trap. The argument by analogy is that living systems contain irreducibly complex parts and therefore could not have evolved gradually.

biological complexity for which imagination fails to perceive an evolutionary origin

level: Comprehensive (3) [ order by level] A term proposed by ID supporter Michael Behe to indicate the possibility that some biological structure could not have evolved because none of the intermediate steps would have been functional. Since only the full structure would work, it must have been designed by an intelligent agent. Biologists claim that no examples of irreducible complexity in the natural world have actually been found.

a system that requires two or more components to function.