Bernard Gert claims that the project of justifying morality is "the primary task" of his major work, 'Morality: Its Nature and Justification'. However, the arguments for and the point of his justification are not entirely clear. This first part of a two-part essay on the justification of morality offers a systematic examination and assessment of Gert's justification. It is argued that Gert's justification is successful, but limited in its scope.