# What is McTaggart's vicious circle problem with the A series?

In The Unreality of Time (1908), J. Ellis McTaggart identifies a fatal vicious circle in the A series of time. What is the problem? The sun rises every day and ever-finer measurements of time are made. The A series is a conceptualisation of this form of time: it is essentially the same thing, so how can it be voided over a case of which-came-first?

The vicious circle is referred to in the 4th paragraph below: The Unreality of Time, page 468

Past, present,and future are incompatible determinations. Every event must be one or the other, but no event can be more than one. This is essential to the meaning of the terms. And, if it were not so, the A series would be insufficient to give us, in combination with the C series, the result of time. For time, as we have seen, involves change, and the only change we can get is from future to present, and from present to past.

The characteristics,therefore, are incompatible. But every event has them all. If M is past, it has been present and future. If it is future,it will be present and past. If it is present, it has been future and will be past. Thus all the three incompatible terms are predicable of each event, which is obviously inconsistent with their being incompatible, and inconsistent with their producing change.

It may seem that this can easily be explained. Indeed it has been impossible to state the difficulty without almost giving the explanation, since our language has verb-forms for the past, present, and future, but no form that is common to all three. It is never true, the answer will run, that M is present, past and future. It is present, will be past, and has been future. Or it is past, and has been future and present, or again is future and will be present and past. The characteristics are only incompatible when they are simultaneous, and there is no contradiction to this in the fact that each term has all of them successively.

But this explanation involves a vicious circle. For it assumes the existence of time in order to account for the way in which moments are past, present and future. Time then must be pre-supposed to account for the A series. But we have already seen that the A series has to be assumed in order to account for time. Accordingly the A series has to be pre-supposed in order to account for the A series. And this is clearly a vicious circle.

• McTaggart seems to think that the meaning of "was, is, will be" depends on the meaning of "A-series," so defending the viability of the A-series using the "was, is, will be" scheme seems circular. I would imagine that an easy enough retort would be that time is not being explained in a circle, but that time is being illustrated by its effect on/role in the logic of "is" in general. Commented Aug 14, 2022 at 12:59
• @KristianBerry The preceding paragraph suggests (to me) the "is" is the authentic temporality of the observer : "The relations which form the A series then must be relations of events and moments to something not itself in the time-series. What this something is might be difficult to say. But, waiving this point, a more positive difficulty presents itself. ..." Commented Aug 14, 2022 at 14:29
• Hmm, I wonder if he was too quick to waive that point, though, then. I hate using scientific information in the wrong way but I wonder how general relativity factors into the A/B distinction in time-series. If something is only relatively past, present, or future, then an event might sustain all three predicates, relativized though, and then not be self-contradictory (nevermind circular, maybe). Commented Aug 14, 2022 at 14:55
• @KristianBerry Different inertial or gravitational frames would make clocks tick faster or slower. If there is absolute simultaneity relative A series would all be focussed on the same present but scaled differently wrt past & future. So nothing past could be in another's future; no contradiction or incompatibility. Proving absolute simultaneity is stymied by unobservability though. Commented Aug 14, 2022 at 15:36
• I doubt that would impress McTaggart. Bergson introduced similar "authentic temporality" under the name of "duration" back in 1889, Husserl pondered "time-consciousness" in 1900s too. McTaggart was an objective idealist, all subject bound constructs were "unreal" to him. And, even "waiving that", explaining them, on his terms, would face the same inconsistency, as he remarks. He is asking for a tenseless explanation of tenses, as long as one plays by his rules there is no escaping circularity. This is ironic becausec he was a Hegelian, and Hegel had change built-in from the start. Commented Aug 14, 2022 at 22:29