given that you’re talking about tropes, i assume you’re dealing specifically with the question of universals or properties.
properties are, basically, attributes of things, or the various ways things can be. and the “question” of properties includes not only concerns as to what things actually count as properties, but also the question as to what kind of thing a “property” is.
as far as the former is concerned, though there is (probably) unanimity among thinkers that
being blue or
taller than are core examples of properties, controversy exists with regards to examples such as
being an apple and so-called ‘disjunctive’ properties, such as
being sharp or the last king of france.
the categories of realism, nominalism, and trope-theory are
ontological categories, which is to say that they are names for points of view on the kind of thing that properties are.
realism (as i understand it - there are often different ways of using these names) proposes that properties are
abstract objects, which is to say that they are not unlike platonic forms: non-corporeal, independently existing, and (traditionally, anyway, thought to be) atemporal (outside of time), and acausal (unable to stand in causal relations to or with anything else). on this view, individual things
instantiate or
exemplify properties - my grey shirt exemplifies the abstract object
greyness, which nonetheless exists independently both of my grey shirt, but also all grey things.
nominalists believe that there are no such things as properties, and that it only seems as though there are as an artifiact of our language: in the end, there are only the words we use to describe things - so-called “properties” are just uses the same word to describe many separate things, and the fact, for example, that both
dog and
blue are nouns does not allows us to conclude that both dogs and
blueness exist in the same way.
trope-theory is a middle-way between what some philosophers consider the ontological extravagance and obscurity of realism, and the explanatory wasteland of nominalism (i.e. some philosophers think that realists believe that there are too many things, but nominalists think there are not enough).
trope theorists believe that there are properties, but they are just (sets of) particulars, such that the property
blue is simply the set or group of all blue things - the group of things that exactly resemble each other with respect to their color. (as opposed to the realist, who would say that two things having the same color is to say that both exemplify or instantiate the same property; and the nominalist who says that we’re just using the same word).
there are many variants of each of these theories, but these are the basics.
a good online resource is the stanford encyclopedia of philosophy:
plato.stanford.edu/
you can look for the entries on “proiperties” and “tropes”, for starters.
good luck.
