Abstraction

Something is abstract if it does not exist at any particular place and time, but instances, or members, of it can exist in many different places and/or times (we say that what is abstract can be multiply instantiated).

If however we just say that what is abstract is what can be instantiated, and that abstraction is simply the movement in the opposite direction to instantiation, we haven't explained everything. That makes 'dog' and 'telephone' abstract ideas, but even small children can recognise a dog or a telephone despite their varying appearances in particular cases. You could say that these concepts are abstractions but are not found to be very abstract in a conceptual sense. We can look at the progression from dog to mammal to animal, and see that animal is more abstract than mammal; but on the other hand mammal is a harder idea to express, certainly in relation to marsupial.

Abstraction in philosophy is the (oft-alleged) process, in concept-formation[?], of recognizing among a number of individuals some common feature, and on that basis forming the concept of that feature. The notion of abstraction is important to understanding some philosophical controversies surrounding empiricism and the problem of universals.

Some research into the human brain claimed that the left and right hemispheres differ in their handling of abstraction. One side handles collections of examples (eg: examples of a tree) whereas the other handles the concept itself.

Reification, also called hypostatization, is the logical fallacy of regarding an abstract concept, such as "society" or "technology" as if it were a concrete thing.

The opposite abstraction is concretisation[?].

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For example, lots of different things have the property of redness: lots of things are red. And we find the relation sitting-on everywhere: many things sit on other things. So the property, redness, and the relation, sitting-on, do not exist in any one particular place. So if we want to say that properties and relations are, or have being, clearly we want to say they have a different sort of being from the sort of being that physical objects, like rocks and trees, have. That accounts for the usefulness of this word 'abstract'. We apply it to properties and relations to mark the fact that if they exist, they do not exist in space or time, but that instances of them can exist in many different places.

On the other hand the apple, and an individual human being, are said to be concrete, and particulars, and individuals.

Confusingly, philosophers sometimes refer to tropes, or property-instances (e.g., the particular redness of this particular apple), as 'abstract particulars[?]'.

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See also: Abstract art, abstraction (computer science).