Colin Gunton has suggested that the crisis of modernity has to do with the question of "One and Many". He argues that classical theology under the influence of Platonism had elevated "One" at the cost of "Many", which led to the modem revolt against "One". A balanced ontology between "One and Many" is thus needed to resolve the modem dilemma. In this article, the author argues that such ontology can be found in Aquinas's notion of participation. In the framework of "creatio ex nihilo", his theory of participation provides a system that unifies all things and yet respects diversity. In this concept of participation, we may find resources for resolving the modem problem of "One and Many".