Abstract entities exist as communicative ideas inherent in the non-abstract entities to which they refer.  In order to prove this, or at least provide plausible reasons for it, I will examine theories of nominalism, Platonism, and immanent form.

Nominalism states that abstract entities such as ideas do not exist except as vocalizations, and that everything in physical reality is a particular, therefore saying that the only things that exist are physical particulars.  This counters the Platonist theory that abstract entities (the forms) exist in a realm of their own, separate from particulars.  However, such a criticism begs the question:  it claims that Platonism is wrong because the forms do not exist as physical particulars; but this alone does not prove that there are no abstract entities.  More to the point, nominalism is flawed in that if physical objects lacked any connecting generality, it would be impossible to speak meaningfully of any sort of identity or relation.  Even if we express abstract entities as vocalizations, at least some of them are vocalizations about actual properties of particulars.  Apparently physical objects require abstract entities.

However, this does not make Platonism true.  In fact, Platonism may merely appeal to ignorance in positing a superior "realm" of intellectable abstract entities. Aristotle’s theory of immanent form seems more credible.  On this view abstract entities exist, but not separate from objects.  They are, on this view, natural aspects of the objects themselves, aspects that make it possible for us to communicate about them.  The fact that there are abstract entities associated with  physical particulars does not eliminate the particularity of their existence which nominalism takes as essential (and even the idea of particularity is an abstract entity!). Our vocalization of abstract entities, then, are inter-subjectively convenient marks for real features abstracted from the world.

Abstract entities are not, therefore, physical things, nor do they exist in a separate realm.  However, the claim that abstract entities are an integral part of every particular object seems more plausible than either denying abstract entities altogether, or giving them a transcendent room of their own.

While it is plausible that the names given to properties associated with physical objects is entirely performed by humans, the fact that those properties exist in the first place seems to come from a source outside of human manipulation.  Inborn abstract properties of physical objects will always remain regardless of the abstract terms and definitions applied to them by humans.  Yet, this idea still does not give any more substance to either nominalism or Platonism, since the inborn abstract entities exist within our perception (i.e.: we know they are there) and exist in our realm and not in another.