historically related (cognates)- As a consequence of systematic changes in pre-Old English times ... be reconstructed- e.g. spec, plec, fac, neg, lig => spy, ply, (de)fy, (de)ny, (re)ly (phonetically ... phonetic changes like N-drop (e.g. an- “not” -> a-), Prefixal Assimilation (e.g. ad- “to, towards” -> ap