Refers to two UK patent cases in which the principle of purposive patent claim construction, i.e., patent claims must be interpreted purposely through the eyes of the person skilled in the art to whom the patent is addressed, was set out. ‘Purposive’ is in essence a recognition that language is an imperfect medium for communicating technical concepts and that therefore allowance should made for inherent difficulties in, or unforeseen implications of, drafting which have resulted in the literal construction not being the one the drafter has obviously intended; i.e., consider the ‘purpose’ of the language and not its literal meaning.