B-theory of time
The B-theory of time is a term, given to one of two positions taken by theorists, in the philosophy of time. The labels, A-theory and B-theory, are derived from the analysis of time and change developed by Cambridge philosopher J. M. E. McTaggart in 'The Unreality of Time' (1908), in which events are ordered via a tensed A-series or a tenseless B-series.
Events (or 'times'), McTaggart observed, may be characterized in two distinct, but related, ways. On the one hand they can be characterized as past, present or future, normally indicated in natural languages such as English by the verbal inflection of tenses or auxiliary adverbial modifiers. Alternatively events may be described as earlier than, simultaneous with, or later than others. Philosophers are divided as to whether the tensed or tenseless mode of expressing temporal fact is fundamental. Those who (like Arthur Prior) take the tensed notions associated with the past, present and future to be the irreducible foundations of temporality and our conceptions of temporal fact, are called A-theorists (similar to presentists). A-theorists deny that past, present and future are equally real, and maintain that the future is not fixed and determinate like the past. Those who wish to eliminate all talk of past, present and future in favour of a tenseless ordering of events are called B-theorists. B-theorists (such as D.H. Mellor and J.J.C. Smart) believe that the past, the present, and the future are equally real.
The past, the present and the future feature very differently in deliberation and reflection. We remember the past and anticipate the future, for example, but not vice versa. B-theorists maintain that the fact that we know much less about the future simply reflects an epistemological difference between the future and the past: the future is no less real than the past; we just know less about it (Mellor 1998). A view was held, for example by Quine and Putnam, that physical theories such as special relativity and latterly Quantum mechanics provide the B-theory with compelling support.
A-theorists on the other hand believe that a satisfactory account of time must acknowledge a fundamental metaphysical difference between past, present and future (Prior 2003). The difference between A-theorists and B-theorists is often described as a dispute about temporal passage or 'becoming'. B-theorists argue that this notion embodies serious confusion about time, while many A-theorists argue that in rejecting temporal 'becoming', B-theorists reject time's most vital and distinctive characteristic. It is common (though not universal) to identify A-theorists' views with belief in temporal passage.
It is also common (though not universal) for B-theorists to be four-dimensionalists, that is, to believe that objects are extended in time as well as in space and therefore have temporal as well as spatial parts. This is sometimes called a time-slice ontology (Clark, 1978).
The debate between A-theorists and B-theorists is a continuation of a metaphysical dispute reaching back to the ancient Greek philosophers Heraclitus and Parmenides. Parmenides thought that reality is timeless and unchanging. Heraclitus, in contrast, believed that the world is a process of ceaseless change, flux and decay. Reality for Heraclitus is dynamic and ephemeral. Indeed the world is so fleeting, according to Heraclitus, that it is impossible to step twice into the same river. The metaphysical issues that continue to divide A-theorists and B-theorists concern the reality of the past, the reality of the future, and the ontological status of the present.
The B-theory of time is also burdened with heavy philosophical problems. On the B-theory, temporal becoming is an entirely subjective phenomenon, and hence not an objective feature of reality. In the absence of minds, every temporal moment and event simply exists tenselessly; there are no tensed facts; no past, present, or future; nothing comes into existence or happens except in the tenseless sense of existing at certain appointed stations as opposed to others. If the mental phenomenon of temporal becoming is an objective feature of reality, this amounts to a denial of the B-theory of time. If the B-theorist bites the bullet, stating that there is no temporal becoming of mental states, then this flies in the face of experience. Sir Arthur Eddington states "We have direct insight into 'becoming' which sweeps aside all symbolic knowledge as on an inferior plane. If I grasp the notion of existence because I myself exist, I grasp the notion of becoming because I myself become. It is the innermost Ego of all that is and becomes."
Temporal philosopher William Lane Craig explains that the B-Theory suffers the same incoherence as all theories that time is illusory, namely, that an illusion or appearance of becoming involves becoming, so that becoming cannot be mere illusion or appearance. The Buddhist can consistently deny the reality of the physical world, since the illusion of physicality does not entail physicality, but this is not the case with temporal becoming. John Laird writes: "Take the supposed illusion of change. This must mean that something, X, appears to change when in fact it does not change at all. That may be true about X; but how could the illusion occur unless there were change somewhere? If there is no change in X, there must be a change in the deluded mind that contemplates X. The illusion of change is actually a changing illusion. Thus the illusion of change implies the reality of some change. Change, therefore, is invincible in its stubbornness; for no one can deny the appearance of change."
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