In the commentaries on Porphyry Boethius on the one hand explains the properties of predication relation at abstract level, from another hand he supplies some ontological options about what can instantiate the terms of the relation, at the end he seems to prefer the similarities as objects of abstract thought. Other options are anyway present, in the commentary on Categories and in the Theological Treatises. One cannot say that the catalogues are complementary or that the same things are catalogued once only, under the same label. On the contrary, objects such as forms, essences and material components can be considered from points of view that are different and not easily comparable. In the present article I will deal with Boethius’ ontological approach not strictly concerned with the Porphyrian text and riddle.