Besides its general set of definitions (the act of separating ingredients; an uncommon or confusing idea, concept, word or quality, being preoccupied or forgetful; a complex visionary work, as in 'abstract art, dental work, etc.), the term 'abstraction' (as well as the expression 'abstract object) are often included in discussions about the correlation between spatiotemporal objects and the non-spatiotemporal ideas such objects refer. In beginning undergraduate philosophy courses, the Platonic or Realist (or Husserlian) example oftentimes given is the 'Idea' behind the 'chair.' The chair changes over time, but the Idea of chair remains outside space and time. The question usually asked is: Do the abstract objects or ideas really exist? Are the abstractions causally related to the objects we see and use? If so, what sort of relationship can they have? Or do such ideas exist only as names (as a part of language) as the nominalists would hold.
Another example that often arises in this discussion is mathematics. Are numbers real? If so, where are they? Such questions bring us to the philosophy of language where the logical analysis of language offers insight into the ontological meaning of abstract objects such as numbers. In the analysis of language, questions about the reality of abstract objects become questions about the logical structure -- the logical validity, the truth or falseness -- of the questions themselves.