the modern meaning of the term "black box" seems to have entered the english language around 1945. in electronic circuit theory the process of network synthesis from transfer functions, which led to electronic circuits being regarded as "black boxes" characterized by their response to signals applied to their ports, can be traced to wilhelm cauer who published his ideas in their most developed form in 1941. although cauer did not himself use the term, others who followed him certainly did describe the method as black-box analysis. vitold belevitch puts the concept of black-boxes even earlier, attributing the explicit use of two-port networks as black boxes to franz breisig in 1921 and argues that 2-terminal components were implicitly treated as black-boxes before that.