The fact that particulars instantiate properties has received two different kinds of explanation employing tropes. On the one hand, Campbell's theory of tropes makes use of just one kind of basic entity. On the other hand, Martin's theory appeals to two different sorts of basic entities. Ontological economy regards notwithstanding, Martin's theory offers a better prospect for the task of giving a satisfactory answer to the main objections that have been posed against trope theory in general. I will discuss some problems concerning regressa and the spatio-temporal location of tropes
