Stemmatics, stemmology or stemmatology is a rigorous approach to textual criticism. Karl Lachmann (1793–1851) greatly contributed to making this method famous, even though he did not invent it. The method takes its name from the word stemma. The Ancient Greek word στέμματα and its loanword in classical Latin stemmata may refer to "family trees". This specific meaning shows the relationships of the surviving witnesses (the first known example of such a stemma, albeit with the name, dates from 1827). The family tree is also referred to as a cladogram. The method works from the principle that "community of error implies community of origin." That is, if two witnesses have a number of errors in common, it may be presumed that they were derived from a common intermediate source, called a hyparchetype. Relations between the lost intermediates are determined by the same process, placing all extant manuscripts in a family tree or stemma codicum descended from a single archetype. The process of constructing the stemma is called recension, or the Latin recensio.