Realism is a view that the statements of a subject matter refer to what is real and therefore could be assigned a definite true or false valuation if we knew what that valuation should be. A realist need not be so for all subject matters but only for a select set of subject matters.
Roughly speaking, realism is one of three philosophical positions (the others being nominalism and conceptualism) on the status of universals -- please refer to the universals tag for a brief overview of what universals are.
Realists believe that universals are primarily derived from the "universal features of singular things" meaning that whatever universals are their ontological location (where they are in the world so to speak) is within or before things-in-themselves. Universals, according to realists, primarily inhere within or are situated before things in the world, as opposed to primarily within our minds as concepts or labels. The position of within is referred to as universalia in re (‘universals in the thing’). The position of before as universalia ante rem (‘universals before the thing’). The latter position, where universals are asserted to exist mind independently and thing independently is more or less that of platonism.
The following are some sources of information on realism.
- Miller, Alexander, "Realism", The Stanford Encyclopedia of Philosophy (Winter 2016 Edition), Edward N. Zalta (ed.), URL = https://plato.stanford.edu/archives/win2016/entries/realism/.
- Wikipedia contributors. (2019, June 14). Philosophical realism. In Wikipedia, The Free Encyclopedia. Retrieved 18:30, July 21, 2019, from https://en.wikipedia.org/w/index.php?title=Philosophical_realism&oldid=901873605