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- This article is about philosophical terms. For the motor
vehicle engines see BMC A-Series engine & BMC
B-Series engine.
A-series and B-series are terms introduced by
the Scottish idealist
philosopher John McTaggart in 1908 which have become
classic terms of reference in modern discussions of the philosophy of time, even outside the analytic tradition.
According to McTaggart, there are two distinct modes in which
all events can be ordered in time. In the first mode, events are
ordered by way of the non-relational singular predicates "is past",
"is present" and "is future." When we speak of time in this way, we
are speaking in terms of a series of positions which run from the
remote past through the recent past to the present, and from the
present through the near future all the way to the remote future.
The essential characteristic of this descriptive modality is that
one must think of the series of temporal positions as
being in continual transformation, in the sense that an
event is first part of the future, then part of the present, and
then past. Moreover, the assertions made according to this modality
imply the temporal perspective of the person who utters them. This
is the A-series of temporal events.
From a second point of view, one can order events according to a
different series of temporal positions by way of two-term relations
which are asymmetric, irreflexive and transitive: "comes before"
(or precedes) and "comes after" (or follows). This is the B-series,
and the philosophy which says all truths about time can be reduced
to B-series statements is the B-Theory of time.
The logic and the linguistic expression of the two series are
radically different. The first is tensed and the
second is tenseless. For example, the assertion
"today it is raining" is a tensional assertion because it depends
on the temporal perspective -- the present -- of the person who
utters it, while the assertion "It rains on the 15th of June, 1996"
is non-tensional because it does not so depend. From the point of
view of their truth-values, the two propositions are
identical (both true or both false) if the first assertion is made
on June 15th, 1996. The non-temporal relation of precedence between
two events, say "E precedes F", does not change over time
(excluding from this discussion the issue of the relativity of
temporal order of causally disconnected events in the theory of
relativity). On the other hand, the character of being "past,
present or future" of the events "E" or "F" does change with time.
In the image of McTaggart: "the passage of time consists in the
fact that terms ever further in the future pass into the
present...or that the present advances toward terms ever farther in
the future. If we assume the first point of view, we speak as if
the B-series slides along a fixed A-series. If we assume the second
point of view, we speak as if the A-series slides along a fixed
B-series.
References
- McTaggart, J.E., The Unreality of Time, in "Mind" ,
1908.
- McTaggart, J.E.,The Nature of Existence, vol. 1-2,
Cambridge University Press, Cambridge, 1968.
- Bradley, F.H., The Principles of Logic, Oxford
University Press, Oxford, 1922.
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