User:SVolcano/Physical object

The material in an object may change over time. For example, a rock may wear away or have pieces broken off it. The object will be regarded as the same object after the addition or removal of material, if the system may be more simply described with the continued existence of the object, than in any other way. The addition or removal of material may discontinuously change the boundary of the object. The continuation of the object's identity is then based on the description of the system by continued identity being simpler than without continued identity.

For example, a particular car might have all its wheels changed, and still be regarded as the same car. There are instances in which a particular car might have some or all parts of it changed and no longer be regarded as the same car. A philosophical dilemma concerning the consistency of identity when material in a particular object is changed over time is discussed in thought experiment, The Ship of Theseus. In this thought experiment, over time, parts of the ship are switched for new ones, replacing the old. Eventually, all the ship's parts have been replaced, leaving us with the question, does the later ship still hold the identity of The Ship of Theseus.

The identity of an object may not split. If an object is broken into two pieces at most one of the pieces has the same identity. An object's identity may also be destroyed if the simplest description of the system at a point in time changes from identifying the object to not identifying it. Also an object's identity is created at the first point in time that the simplest model of the system consistent with perception identifies it.

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A physical body is an enduring object that exists throughout a particular trajectory of space and orientation over a particular duration of time, and which is located in the world of physical space (i.e., as studied by physics). This contrasts with abstract objects such as mathematical objects which do not exist at any particular time or place.

Examples are a cloud, a human body, a banana, a billiard ball, a table, or a proton. This is contrasted with abstract objects such as mental objects, which exist in the mental world, and mathematical objects. Other examples that are not physical bodies are emotions, the concept of "justice", a feeling of hatred, or the number "3". Non-physical bodies are known by using rationality in the Epistemological view, Rationalism. In contrast, identifying physical bodies rely on empirical observation, using sensory faculties. In the philosophical tradition, physical bodies are known a-posteriori while non-physical bodies are known a-priori. In some philosophies, like the idealism of George Berkeley, a physical body is a mental object, but still has extension in the space of a visual field.