Therefore <there are trees> possibly exists in a world without concrete entities

A parallel “easy argument” can be given for the abstractness of at least some propositions. &lt;2+2=4&gt; does not entail the existence of concrete entities. So it is possible for it to be true (and so to exist) in the absence of concrete entities. Thus, it is possibly abstract. Assuming, contra Linksy and Zalta (1996), that abstractness is, necessarily, an essential feature of abstract entities, then it follows that &lt;2+2=4&gt; is in fact abstract. One might want to extend such arguments to c