Substratum and bundle theories The distinction between a concrete particular and the attributes it has or possesses plays a pivotal role in metaphysical thinking. As we have seen, not all metaphysicians recognize the distinction. The austere nominalist insists that in the strict sense there are no attributes; but for those philosophers, metaphysical realists and trope theorists alike, who recognize the distinction, it is an important distinction, one between what appear to be two irreducibly different ontological categories. So far, we have examined the distinction from the side of attributes, but debate over the nature of concrete particulars has been every bit as heated as that over the nature of attributes. I want to begin our discussion of this debate by considering two different theories about the nature of concrete particulars. Our discussion will lead us to consider a third theory; but by focusing on the dialectical opposition between the first two theories, we will come to appreciate the difficulties that confront us in the attempt to provide a metaphysical account of the concept of a concrete particular.