Many recent studies propose that symbolon and synthēma are synonymous in the writings of Proclus. However, his Platonic Theology contains reliable evidence to put this opinion to doubt. The goal of this research is to determine the meaning of both terms from the contexts of their usage, engaging the textual analysis and the following philosophical reconstruction. As distinguished from a symbol, a synthēma has substantial nature, is stable and remains invariable when is discovered at different levels of the ontological hierarchy. In the Platonic Theology, a symbol is often considered in terms of the hierarchic level, where it appears: in the material world, it is corporeal; among numbers, it is ontologically irrelevant, the intelligible realm contains its proper symbols as well. A significant difference between symbolon and synthēma is related to the dialectics of participation: synthēma in an object keeps it on an unparticipated level, while a symbol implies further participation to a symbolic object. Finally