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By Branch / Doctrine > Metaphysics
Metaphysics is the branch of philosophy concerned with the nature of existence, being and the world. Arguably, metaphysics is the foundation of philosophy: Aristotle calls it "first philosophy" (or sometimes just "wisdom"), and says it is the subject that deals with "first causes and the principles of things".
It asks questions like: "What is the nature of reality?", "How does the world exist, and what is its origin or source of creation?", "Does the world exist outside the mind?", "How can the incorporeal mind affect the physical body?", "If things exist, what is their objective nature?", "Is there a God (or many gods, or no god at all)?"
Originally, the Greek word "metaphysika" (literally "after physics") merely indicated that part of Aristotle's oeuvre which came, in its sequence, after those chapters which dealt with physics. Later, it was misinterpreted by Medieval commentators on the classical texts as that which is above or beyond the physical, and so over time metaphysics has effectively become the study of that which transcends physics.
Aritstotle originally split his metaphysics into three main sections and these remain the main branches of metaphysics:
Metaphysics has been attacked, at different times in history, as being futile and overly vague, particularly by David Hume, Immanuel Kant and A.J. Ayer. It may be more useful to say that a metaphysical statement usually implies an idea about the world or the universe, which may seem reasonable but is ultimately not empirically verifiable, testable or provable.
Existence (the fact or state of continued being) is axiomatic (meaning that it does not rest upon anything in order to be valid, and it cannot be proven by any "more basic" premises) because it is necessary for all knowledge and it cannot be denied without conceding its truth (a denial of something is only possible if existence exists). "Existence exists" is therefore an axiom which states that there is something, as opposed to nothing.
Consciousness is the faculty which perceives and identifies things that exist. In his famous formulation "Cogito ergo sum" ("I think therefore I am"), René Descartes argued that consciousness is axiomatic, because you cannot logically deny your mind's existence at the same time as using your mind to do the denying.
However, what Descartes did not make clear is that consciousness is the faculty that perceives that which exists, so it requires something outside of itself in order to function: it requires, and is dependent upon, existence. The primacy of existence states that existence is primary and consciousness is secondary, because there can be no consciousness without something existing to perceive. Existence is independent of, makes possible, and is a prerequisite of consciousness. Consciousness is not responsible for creating reality: it is completely dependent upon reality.
Early debates on the nature of matter centred on identifying a single underlying principle (Monism): water was claimed by Thales, air by Anaximenes, Apeiron (meaning "the undefined infinite") by Anaximander, and fire by Heraclitus. Democritus conceived an atomic theory (Atomism) many centuries before it was accepted by modern science.
The nature of the mind and its relation to the body has also exercised the best brains for millennia. There is a large overlap here with Philosophy of Mind, which is is the branch of philosophy that studies the nature of the mind, mental events, mental functions, mental properties and consciousness, and their relationship to the physical body.
In the 17th Century, Descartes proposed a Dualist solution called Substance Dualism (or Cartesian Dualism) whereby the mind and body are totally separate and different: the mental does not have extension in space, and the material cannot think.
Idealists, like Bishop George Berkeley and the German Idealist school, claim that material objects do not exist unless perceived (Idealism is essentially a Monist, rather than Dualist, theory in that there is a single universal substance or principle).
Baruch Spinoza and Bertrand Russell both adopted, in different ways, a dual-aspect theory called Neutral Monism, which claims that existence consists of a single substance which in itself is neither mental nor physical, but is capable of mental and physical aspects or attributes.
In the last century, science (particularly atomic theory, evolution, computer technology and neuroscience) has demonstrated many ways in which mind and brain interact in a physical way, but the exact nature of the relationship is still open to debate. The dominant metaphysics in the 20th Century has therefore been various versions of Physicalism (or Materialism), a Monist solution which explains matter and mind as merely aspects of each other, or derivatives of a neutral substance.
The world contains many individual things (objects or particulars), both physical and abstract, and what these things have in common with each other are called universals or properties. Metaphysicians are interested in the nature of objects and their properties, and the relationship between the two (see the sections on Realism and Nominalism).
The problem of universals arises when people start to consider in what sense it is possible for a property to exist in more than one place at the same time (e.g. a red car and a red rose). It seems clear that there are many red things, for example, but is there an existing property of 'redness'? And if there is such a thing as 'redness', what kind of thing is it? See the section on Realism for a further discussion of this.
Any object or entity is the sum of its parts (see Holism). The identity of an entity composed of other entities can be explained by reference to the identity of the building blocks, and how they are interacting. A house can be explained by reference to the wood, metal, and glass that are combined in that particular way to form the house; or it could be explained in terms of the atoms that form it (see the sections on Atomism and Reductionism).
Identity is whatever makes an entity definable and recognizable, in terms of possessing a set of qualities or characteristics that distinguish it from entities of a different type (effectively, whatever makes something the same or different). Thus, according to Leibniz, if some object x is identical to some object y, then any property that x has, y will have as well, and vice versa (otherwise, by definition, they would not be identical).
Aristotle's Law of Identity (or the Axiom of Identity) states that to exist, an existent (i.e. an entity that exists) must have a particular identity. A thing cannot exist without existing as something, otherwise it would be nothing and it would not exist. Also, to have an identity means to have a single identity: an object cannot have two identities at the same time or in the same respect. The concept of identity is important because it makes explicit that reality has a definite nature, which makes it knowable and, since it exists in a particular way, it has no contradictions (when two ideas each make the other impossible).
Change is the alteration of identities, whether it be a stone falling to earth or a log burning to ash. For something to change (which is an effect), it needs to be acted on (caused) by a previous action. Causality is the law that states that each cause has a specific effect, and that this effect is dependent on the initial identities of the agents involved.
We are intuitively aware of change occurring over time (e.g. a tree loses a leaf). The Ancient Greeks took some extreme positions on the nature of change: Parmenides denied that change occurs at all, while Heraclitus thought change was ubiquitous.
Currently there are three main theories which deal with the problem of change:
A traditional Realist position is that time and space have existence independent from the human mind. Idealists, however, claim that space and time are mental constructs used to organize perceptions, or are otherwise unreal.
Descartes and Leibniz believed that, without physical objects, "space" would be meaningless because space is the framework upon which we understand how physical objects are related to each other. Sir Isaac Newton, on the other hand, argued for an absolute space ("container space"), which can continue to exist in the absence of matter. With the work of Sir Albert Einstein, the pendulum swung back to relational space in which space is composed of relations between objects, with the implication that it cannot exist in the absence of matter.
Although Parmenides denied the flow of time completely in ancient times, echoed more recently by the British Idealist J.M.E. McTaggart (1866 - 1925), much debate in both philosophy and physics has centred on the direction of time ("time's arrow"), and whether it is reversible or symmetrical. As for whether objects persist over time, then the endurantism / perdurantism dichotomy described above applies.
Theology is the study of God and the nature of the Divine. This is sometimes considered a whole separate branch of philosophy, the Philosophy of Religion (see that section for more detail). It asks questions like:
A necessary fact is true across all possible worlds (that is, we could not imagine it to be otherwise). A possible fact is one that is true in some possible world, even if not in the actual world. This idea of possible worlds was first introduced by Gottfried Leibniz, although others have dealt with it in much more detail since, notably the American analytic philosopher David Lewis (1941 - 2001) in his theory of Modal Realism.
The concept of necessity and contingency (another term used in philosophy to describe the possibility of something happening or not happening) is also central to some of the arguments used to justify the existence or non-existence of God, notably the Cosmological Argument from Contingency (see the section on Philosophy of Religion for more details).
Some philosophers hold that there are abstract objects (such as numbers, mathematical objects and fictional entities) and universals (properties that can be possessed by multiple objects, such as "redness" or "squareness"), both of which which are outside of space and time and/or are causally inert.
On the other hand, (Nominalism), holds that there is really no such thing as abstract objects, which really exist only as names, because a single object cannot exist in multiple places simultaneously.
Moderate Realism, as espoused by Aristotle among others, tries to find some middle ground between Nominalism and Realism, and holds that there is no realm as such in which universals exist, but rather they are located in space and time wherever they happen to be manifest. Conceptualism, the doctrine that universals exist only within the mind and have no external or substantial reality, is also an intermediate solution.
Other positions such as Formalism and Fictionalism do not attribute any existence to mathematical entities, and are anti-Realist.
The Philosophy of Mathematics overlaps with metaphysics in this area.
Determinism is the philosophical proposition that every event, including human cognition, decision and action, is causally determined by an unbroken chain of prior occurrences.Thus, there is at any instant only one physically possible future, and no random, spontaneous, mysterious or miraculous events ever occur.
This posits that there is no such thing as Free Will, where rational agents can exercise control over their own actions and decisions. Incompatibilists (or Hard Determinists) like Baruch Spinoza, view determinism and free will as mutually exclusive. Others, labelled Compatibilists (or Soft Determinists), like Thomas Hobbes, believe that the two ideas can be coherently reconciled.
It should be noted that Determinism does not necessarily mean that humanity or individual humans have no influence on the future (that is known as Fatalism), just that the level to which human beings have influence over their future is itself dependent on present and past.
Cosmology is the branch of metaphysics that deals with the world as the totality of all phenomena in space and time. Historically, it was often founded in religion; in modern use it addresses questions about the world and the universe which are beyond the scope of physical science. Cosmogony deals specifically with the origin of the universe, but the two concepts are closely related.
Pantheists, such as Spinoza, believe that God and the universe are one and the same. Panentheists, such as Plotinus, believe that the entire universe is part of God, but that God is greater than the universe. Deists, such as Voltaire, believe that God created the universe, set everything in motion, and then had nothing more to do with it. See the section on Philosophy of Religion for more details.
Under the heading of Metaphysics, the major doctrines or theories include:
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