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The B-theory (tenseless) treats all times as metaphysically equivalent with no genuine passage; the A-theory (tensed) posits genuine temporal flow where only the present is uniquely real. This fundamental division determines whether time involves real becoming or merely logical and causal ordering within a static four-dimensional block.
Study arguments from physics (relativity theory), language (tense and temporal reference), and phenomenology (temporal experience) for each view. Examine hybrid theories that combine A and B features.
Assuming relativity or modern physics definitively settles the A/B-theory debate. Conflating the A/B-theory with presentism/eternalism (which are distinct but related positions).
From your prerequisite work in the philosophy of time and the A-theory/B-theory distinction, you know the basic contrast: the B-theory says all times are equally real, arranged in a permanent "block" of past, present, and future, ordered by the earlier/later-than relation. The A-theory says there is genuine temporal flow — events are not just earlier or later than each other but are *really* past, present, or future, and these properties change. Now let's build sharper intuitions about what's actually at stake.
The B-theory's central claim is that temporal language is misleading. When you say "the battle *was* fought yesterday," B-theorists say this is just a tensed way of saying that the battle is earlier-than your utterance — a permanent, unchanging relational fact. Time is like space: just as every spatial location is equally real, every temporal location is equally real. The year 1066 is "past" only relative to us, just as London is "north" only relative to somewhere south of it. On this view, temporal becoming — the sense that the present is constantly advancing, that events genuinely come to be and then cease — is a psychological illusion, not a feature of reality.
The A-theory insists this analysis loses something essential. A-properties — being past, present, or future — are not mere relations to other times; they are intrinsic, monadic properties of events that genuinely change. The Battle of Hastings was future, then present, then past, and these transitions are real features of the world, not just perspectival descriptions. The present moment is not just the time at which you happen to be located; it is *metaphysically special*. This is the intuitive pull of the A-theory: the "flow" of time, the sense that now is here and then is gone, seems to be something the B-theory flatly denies.
The crucial point your prerequisites noted — that these theories are distinct from presentism/eternalism — is worth unpacking. Presentism says only present entities exist; eternalism says past, present, and future entities all exist. These are claims about what exists. A-theory and B-theory are claims about what temporal properties are fundamental and whether time flows. Many A-theorists are presentists, but the A-theory is compatible with holding that past and future things also exist, as long as you maintain that the present is ontologically privileged. Similarly, a B-theorist might be an eternalist (the block universe view), but the logical connections are not forced. Keeping these distinctions sharp is essential for evaluating arguments in temporal metaphysics that trade on moving between them.
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