The problem of universals is the problem of unity in differences. Nevertheless, how many different things may form a unity? In general, realists say that this apparent unity is grounded by common properties of things, whereas extreme nominalists reject the existence of properties at all, and seek other ways to explain this unity. Now, the trope theory seems to be a plausible way out of this dilemma. It holds, against extreme nominalism, that there are properties, but - in contrast to plain realism - takes them as particular. For this reason the trope theory is sometimes called moderate nominalism. In this book I argue that the category of tropes, that is abstract particulars, could be and actually has been adopted not only by nominalists but also realists. The kind of realism accepting both tropes and universals is aptly called moderate realism. Tropes, therefore, do not belong to the nominalistic trope theories only. To prove this, first, I provide a systematic analysis of the problem of universals and the category of abstract particulars, and then carry out historical investigations into three theories combining tropes and different kinds of universals, formulated by Roman Ingarden, St Thomas Aquinas and G. W. F. Hegel. In the first chapter, I discuss the problem of universals and distinguish it from the two closely connected, yet distinct issues: the problem of the meaning of general terms on the one hand, and the problem of the existence of non-spatiotemporal entities on the other. All these issues were regrettably blurred in the Platonic tradition, continued in the twentieth century by Bertrand Russell. In order to distinguish universals and predicates I propose a detailed analysis of the so-called picture theory of language, embracing three distinct claims: that predicates are true about things in virtue of some properties (I propose to call it proprietarity), that such properties are the same in each case (homogeneity) and finally that such properties are universal (universality). In the second chapter, I distinguish three concepts of universals: abstract, determinable and concrete. First, abstract universals are simply common properties widely discussed in the analytic ontology. As it seems, they fit best the explanation of the problem of strict resemblance. Second, determinable universals, less discussed nowadays, are those which answer the problem of generic resemblance. I propose a new analysis of determinables based on the concept of qualitative dependency, an analogous to traditional existential dependency. I call determinables the aspects of things and properties. I argue that for many philosophers, especially scholastics and phenomenologists, universals were primarily determinable aspects, not determinate properties. Finally, and probably most controversially, I try to reintroduce the category of concrete universals, formulated by Hegel and British and American neo-Hegelians. In contrast to abstract universals, concrete universals are not understood as common properties but rather as common wholes. Both concepts of universals assume the notion of existential dependency, but in the case of concrete universals, its direction is reversed. Abstract properties depend on their things, whereas things are dependent on their concrete wholes. Members of concrete universals do not share common properties and even are not necessarily similar; they are different ontological expressions of the same object instead. In chapter three, I examine the concept of a trope and show that the two previously distinguished concepts of universals, namely determinable aspects and concrete wholes, are fully compatible with the assumption that all properties are particular. There are, therefore, two general kinds of realistic theories of tropes, namely one combining abstract particulars with determinable universals and another joining tropes and concrete universals. In the following chapters, I provide some historical examples of such theories. In chapter four, I investigate Roman Ingarden’s theory of universals. On the one hand he openly claimed that all properties are particulars, on the other he accepted universals understood as determinable Platonic ideas. I argue, however, following Gustav Bergmann’s argumentation against Frege and Husserl, that Ingarden’s insistence on the transcendent character of ideas results in hidden nominalism of his system. It is so since determinables not literally shared by many tropes cannot be true universals. Next, I focus on St Thomas Aquinas’s theory of universals. He also openly admitted that all accidents are individual, and claimed that there are determinable universals. Since Aquinas did not write much on universals directly, I suggest inferring his view from his theory of cognition, in which he assumed the identity of the content in mind with the general nature in thing. In contrast to Ingarden, Aquinas believed that universals somehow are in tropes, not beyond them. He claimed that universals are potentially contained in particular natures and can be actualised by the human intellect in the process of abstraction. I suggest that Aquinas’s view might be interpreted with the help of the concept of qualitative dependency of determinables, introduced in chapter two. Finally, in the last chapter, I reconstruct Hegel’s theory of universals and argue that it also gave a room for the existence of tropes. I contrast my own interpretation of concrete universals, based primarily on Josiah Royce’s and Ivan Il’in’s commentaries, with two other readings, in which Hegelian universals are understood as merely determinables or natural kinds. I argue that only the interpretation of concrete universals as literally universal substance completely covers all Hegel’s embarrassing claims on universals. I also try to read the classic early trope theory of G. F. Stout as a kind of Hegelian theory of tropes. The famous natural classes of tropes are strikingly close to concrete universals. Perhaps then the very category of abstract particulars has a hidden Hegelian genealogy. As a result, it seems that tropes should not be thought as an exclusively nominalistic invention. They can be found in many philosophers long before analytic discussions in the twentieth century, and usually were combined with different kinds of universals. The contemporary nominalistic theory of tropes is merely one of the many theories adopting abstract particulars.