section_path: Basic concepts/Concrete and abstract objects
section_name: Concrete and abstract objects
paragraph_text: Concrete and abstract objects
  
  Concrete objects are entities that exist in space and time, such as a tree, a car, and a planet. They have causal powers and can affect each other, like when a car hits a tree and both are deformed in the process. Abstract objects, by contrast, are outside space and time, such as the number 7 and the set of integers. They lack causal powers and do not undergo changes. It is controversial whether or in what sense abstract objects exist and how people can know about them.
  
  Concrete objects encountered in everyday life are complex entities composed of various parts. For example, a book is made up of two covers and pages between them. Each of these components is itself constituted of smaller parts, like molecules, atoms, and elementary particles. Mereology studies the relation between parts and wholes. One position in mereology says that every collection of entities forms a whole. According to a different view, this is only the case for collections that fulfill certain requirements, for instance, that the entities in the collection touch one another. The problem of material constitution asks whether or in what sense a whole should be considered a new object in addition to the collection of parts composing it.
  
  Abstract objects are closely related to fictional and intentional objects. Fictional objects are entities invented in works of fiction. They can be things, like the One Ring in J. R. R. Tolkien 's book series The Lord of the Rings, and people, like the Monkey King in the novel Journey to the West. Some philosophers say that fictional objects are one type of abstract object, existing outside space and time. Others understand them as artifacts that are created as the works of fiction are written. Intentional objects are entities that exist within mental states, like perceptions, beliefs, and desires. For example, if a person thinks about the Loch Ness Monster then the Loch Ness Monster is the intentional object of this thought. People can think about existing and non-existing objects, making it difficult to assess the ontological status of intentional objects.