A real entity has many aspects. It can be apprehended with various concepts such as pine, tree, earthen, substance, existent, and object. People can extract a certain aspect of an entity by means of words. According to Dignāga, this extraction is possible only through excluding the other meanings. His claim implies that this extraction is impossible in the framework of realism, in which universals are posited in accordance with their corresponding concepts. According to Dignāga, a co-referential expression sad dravyam cannot be explained in the realist view, because there is a difference in level between the substratum and the property. In other words, the expression would become figurative (aupacārika, bhākta). If one forcedly pulled down the properties to the ground level, undesirable consequences such as contradiction (virodha) between properties or confused perception (mecakadarśana) would follow. It is impossible to extract a single property when many properties cohabit in an entity. The theory of exclusion (apoha), however, does not run into this problem, because exclusion is not a substance (adravya). Many exclusions, such as the exclusion of non-pots and so on, can cohabit in an entity. A certain exclusion can be extracted in accordance with the difference of the excluded objects. Therefore, Dignāga claims that a certain aspect of a real entity is apprehended in the world by excluding the other meanings.
