Property (philosophy)

At least since Plato, properties are viewed by numerous philosophers as universals, which are typically capable of being instantiated by different objects. Philosophers opposing this view regard properties as particulars, namely tropes.[1]

A realist about properties asserts that properties have genuine, mind-independent existence.[1] One way to spell this out is in terms of exact, repeatable, instantiations known as universals. The other realist position asserts that properties are particulars (tropes), which are unique instantiations in individual objects that merely resemble one another to various degrees. Transcendent realism, proposed by Plato and favored by Bertrand Russell, asserts that properties exist even if uninstantiated.[1] Immanent realism, defended by Aristole and David Malet Armstrong, contends that properties exist only if instantiated.[1]

The anti-realist position, often referred to as nominalism claims that properties are names we attach to particulars. The properties themselves have no existence.

Properties are often classified as either categorical and dispositional.[2][3] Categorical properties concern what something is like, e.g. what qualities it has. Dispositional properties, on the other hand, involve what powers something has, what it is able to do, even if it is not actually doing it.[2] For example, the shape of a sugar cube is a categorical property while its tendency to dissolve in water is a dispositional property. For many properties there is a lack of consensus as to how they should be classified, for example, whether colors are categorical or dispositional properties.[4][5]

According to categoricalism, dispositions reduce to causal bases.[6] On this view, the fragility of a wine glass, a dispositional property, is not a fundamental feature of the glass since it can be explained in terms of the categorical property of the glass's micro-structural composition. Dispositionalism, on the other hand, asserts that a property is nothing more than a set of causal powers.[4] Fragility, according to this view, identifies a real property of the glass (e.g. to shatter when dropped on a sufficiently hard surface). Several intermediary positions exist.[4] The Identity view states that properties are both categorical(qualitative) and dispositional; these are just two ways of viewing the same property. One hybrid view claims that some properties are categorical and some are dispositional. A second hybrid view claims that properties have both a categorical(qualitative) and dispositional part, but that these are distinct ontological parts.

Property dualism: the exemplification of two kinds of property by one kind of substance

Property dualism describes a category of positions in the philosophy of mind which hold that, although the world is constituted of just one kind of substance—the physical kind—there exist two distinct kinds of properties: physical properties and mental properties. In other words, it is the view that non-physical, mental properties (such as beliefs, desires and emotions) inhere in some physical substances (namely brains).

This stands in contrast to physicalism and idealism. Physicalism claims that all properties, include mental properties, ultimately reduce to, or supervene on, physical properties.[7] Metaphysical idealism, by contrast, claims that "something mental (the mind, spirit, reason, will) is the ultimate foundation of all reality, or even exhaustive of reality."[8]

An intrinsic property is a property that an object or a thing has of itself, independently of other things, including its context. An extrinsic (or relational) property is a property that depends on a thing's relationship with other things. The latter is sometimes also called an attribute, since the value of that property is given to the object via its relation with another object. For example, mass is a physical intrinsic property of any physical object, whereas weight is an extrinsic property that varies depending on the strength of the gravitational field in which the respective object is placed. other examples are the name of a person (an attribute given by the person's parents) and the weight or mass of the person.

In classical Aristotelian terminology, a property (Greek: idion, Latin: proprium) is one of the predicables. It is a non-essential quality of a species (like an accident), but a quality which is nevertheless characteristically present in members of that species. For example, "ability to laugh" may be considered a special characteristic of human beings. However, "laughter" is not an essential quality of the species human, whose Aristotelian definition of "rational animal" does not require laughter. Therefore, in the classical framework, properties are characteristic qualities that are not truly required for the continued existence of an entity but are, nevertheless, possessed by the entity.

A property may be classified as either determinate or determinable. A determinable property is one that can get more specific. For example, color is a determinable property because it can be restricted to redness, blueness, etc.[9] A determinate property is one that cannot become more specific. This distinction may be useful in dealing with issues of identity.[10]

Impure properties are properties that, unlike pure properties, involve reference to a particular substance in their definition.[11] So, for example, being a wife is a pure property while being the wife of Socrates is an impure property due to the reference to the particular "Socrates".[12] Sometimes, the terms qualitative and non-qualitative are used instead of pure and impure.[13] Most but not all impure properties are extrinsic properties. This distinction is relevant for the principle of identity of indiscernibles, which states that two things are identical if they are indiscernible, i.e. if they share all their properties.[11] This principle is usually defined in terms of pure properties only. The reason for this is that impure properties are not relevant for similarity or discernibility but taking them into consideration nonetheless would result in the principle being trivially true.[11] Another application of this distinction concerns the problem of duplication, for example, in the Twin Earth thought experiment. It is usually held that duplication only involves qualitative identity but perfect duplicates can still differ concerning their non-qualitative or impure properties.[13]

Daniel Dennett distinguishes between lovely properties (such as loveliness itself), which, although they require an observer to be recognised, exist latently in perceivable objects; and suspect properties which have no existence at all until attributed by an observer (such as being suspected of a crime).[14]