Note that what is abstract in this sense tend to be ideas, fantasies, imaginations, whether or not - like mathematics or metaphysics or ethics - these abstract ideas are deemed to be applicable to empirically given reality.

One important limitation and danger of abstract things - which is also the reason for its strengths - is that they derive from disregarding certain aspects of real things.

The things that are disregarded are normally supposed to be irrelevant to the truth or falsity of the judgment that so-and-so is or satisfies an abstraction of a certain kind.

One important class of abstractions are natural kinds, which shows that what may be derived by abstraction - disregarding all features and all individual distinctions that are irrelevant to whether or not something is, say, a lion - still may be quite real and practically useful (if true).