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Used as an adjective, the term void means empty, unoccupied or vacant; as a noun, it means that which is void and particularly an empty space. In the latter sense it admits of various meanings: (1) geometrical space or pure extension (of one or two or more dimensions) that is the object of geometry; (2) psychological space, considered as infinitely extended and empty, the indispensable receptacle of bodies and absolutely penetrable by them; and (3) physical space, conceived as the basis for real spatial relations between bodies and as the referential system for their position and motion.

History. The Greek philosopher parmenides (c. 540c. 475 b.c.) formulated the so-called Eleatic principle: "Being is, non-being is not." This principle was challenged by the Greek atomists (c. 400 b.c.), who claimed that nonbeing (the vacuum or void) exists, just as being (the plenum or "full") exists; in other words, they accepted the real existence of empty space or of the void. Medieval and scholastic philosophers, following aristotle, generally equated the void with nonbeing and thus rejected its real existence.

Among modern philosophers, R. descartes (15961650), for whom extension constituted the essence of material bodies, regarded an extended void as contradiction and an absurdity. Yet his contemporary, P. gassendi (15921655), accepted the existence of an eternal and infinite space in which God created the finite world. Isaac Newton (16421727) and Samuel Clarke (16751729) admitted the reality of absolute space in which ordinary bodies are located and move; as opposed to this, G.W. leibniz (16461716) rejected the reality of an independently existing space because of the contradictions it implied. For rather different reasons i. kant (17241804) denied that real space and time have an independent existence and accepted them only as a priori forms of intuition. Many scientists of recent times verbally admit the existence of a void as well as of action at a distance, but implicitly contradict themselves when they subsequently attribute properties and activities to this empty space.

Reality. Does anything real correspond to the void or empty space conceived by the imagination? If the void is considered as the general receptacle of bodies, it would appear that this empty space is infinitely extended; for example, it must function as the receptacle of any new bodies that could be added to those that already exist, and this can be conceived as going on ad infinitum. It is difficult to attribute reality to such an infinitely extended space, particularly when its only function is to serve as a receptacle for perceptible bodies and when it is in no way involved in their existence and activities. The difficulty becomes more acute when one considers that the same argument that requires this space to be real also demands another real container as the receptacle of this real space, followed by a third container, and so on. The result is an infinite series of spaces, which is itself absurd. Thus void understood in this sense cannot be a real being.

Nevertheless the void so conceived does exist in the imagination and can be termed a being of reason with a foundation in reality. This expression means that the term void can be used in meaningful sentences that state a judgment concerning reality. For example, it is meaningful to speak of a void existing between celestial bodies in the sense that the universe is not filled with such bodies in a continuous fashion. Likewise, one can say that the void extends to infinity in the sense that the existing cosmos can expand indefinitely. It is meaningful also to state that this void is three dimensional, understanding this to mean that the bodies in the universe are three dimensional. It should be noted, however, that the space created by the imagination is not empty in the strict sense; rather it is a kind of obscure threedimensional continuum in which different parts can be distinguished, and wherein positions and motions can be attributed to the imagined bodies.

Bibliography: v.e. smith, The General Science of Nature (Milwaukee 1958). p. hoenen, Cosmologia (4th ed. Rome 1949). p.h. van laer, Actio in distans en aether (Utrecht 1947).

[p. h. van ler]