This book proposes to investigate the arts from the inside, namely to consider, first and foremost, what artists do to create their works in order to proceed fruitfully in the direction of their evaluation and explanation. To this end, it develops a philosophical inquiry that examines the ground zero of the arts, their common foundations, namely the rules for artistic creation, the processes that involve artists in their activities, the forms that they can or cannot achieve. This proposal and its outline for a rule-based ontology of the arts addresses four themes: the relationship between human nature and artistic practices, the features of art-making, the conception of artworks as structures, and the social nature of the arts.