Hans Reichenbach argues for the causality and causal chain to define a topological coordinative definition of time order. Here is an excerpt from his textbook, The Philosophy of Space and Time, Dover(1957), pp.138

Another example: We throw a stone from A to B. If we mark the stone with a piece of chalk at A, it will carry the same mark when it strives at B (event E2). If we mark the stone only on its arrival at B, then the stone leaving A (event E1) has no mark.

This distinction appears trivial, but it is extremely significant. A theory of causality which ignores this elementary difference has neglected the most essential aspect. The procedure which we have described is used constantly in everyday life to establish a time order, and we have no other method in many scientific investigations where time intervals are too short to be directly observable. We must therefore include the mark principle in the foundations of the theory of time.

We have in the above principle a criterion for causal order that does not employ the direction of time, and we can therefore use it in our definition of time order. There exists a topological coordinative definition for time order. We can base it in general on the concept of the causal chain, in which the order of events corresponds to the order of time. Occasionally one speaks also of signals or signal chains. It should be noted that the word "signal" means the transmission of signs and hence concerns the very principle of causal order which we have discussed.

My issue is, isn't he implicitly assuming prior and later time, i.e, the time order in defining the causal events? Isn't the mark principle takes into account the time ordering? How is this decoupled from the time ordering?

  • I did post the same question at Physics SE since I have no idea which place this should fit. physics.stackexchange.com/q/763698/193484 May 12, 2023 at 9:25
  • He says: mark a stone at A and mark a stone at B, whichever mark appears in both places is the one that we shall say "happened earlier". How is he implicitly assuming time direction in his marking?
    – Conifold
    May 12, 2023 at 10:12
  • What's going on in Reichenbach's mind is obvious, and he makes an effort ta scratch that itch and I give it an 8 outta 10 for taking the issue seriously enough, but for some reason I don't think he actually solves the problem or is it that he's merely defining it for future gens. Both? 🥰 May 12, 2023 at 10:27
  • Time is a flat circle... You may find this answer relevant: 'Is the idea of a causal chain physical (or even scientific)?' philosophy.stackexchange.com/questions/70930/…
    – CriglCragl
    May 12, 2023 at 12:53
  • Einstein would've been a big help! Alas he's dead and his reincarnation it seems hasn't played his cards right! Woe is us, I mean, me! 🤫 Ordering seems ta have an ethical flavor to it. Is that significant? May 14, 2023 at 8:21

3 Answers 3


Here's my attempt:

Huw Price has said of Reichenbach in general that he was talking about, and made clear(ish) that, the local thermodynamic gradient does not give a global direction to time. Here's one reference I can find to that

Huw Price: Philosophy of Time, Boltzmann Brains, and Retrocausality, Robinson's Podcast #58 (Youtube link)

While I don't have the wider knowledge to ascertain exactly what Reichenbach is doing here, it doesn't seem like he is ascribing it to time itself. It seems more of a local method to determine causal order.

An objective directionality to time is a fairly niche position, and for my money the most successful proponents of it use common sense, everyday experience as evidence. For precisely the reason that an objective, encompassing directionality is hard to establish empirically/scientifically. The dominant position seems to be time has no inherent/objective direction; the low entropy big bang suffices to explain all directionality. It would seem out of character for one of the titans of philosophy of science to make the full connection your title does. So I have to assume Reichenbach is being more modest than ascribing directionality to time itself.

  • I don't know what you have been reading, but the objective directionality of time is the dominant position philosophy. In fact, I don't know of any philosopher who takes the alternative position. May 12, 2023 at 22:56
  • @DavidGudeman I think by "objective" the OP means "intrinsic" and "global" direction. The thermodynamic arrow is objective enough, but an artifact of dynamics and subverted in strong gravitational fields. General relativity is taken to suggest that not only is time not inherently directional, but is not even a thing separate from space. So intrinsic direction does not make much sense. Since analytic philosophers generally defer to science it would not surprise me if a majority subscribes to eternalism, B-theory, etc.
    – Conifold
    May 13, 2023 at 0:41
  • @Conifold, so the idea that the mind sort of moves along a pre-existing timeline is considered subjective time? I wouldn't use the word in that way, but I guess it kind of makes sense. May 13, 2023 at 1:04
  • @DavidGudeman David Albert, Harvey Brown, David Wallace, seemingly due. The 2nd law requires something "over and above the laws" according to Brown--very low entropy initial conditions. Initial conditions are not time itself in most parlance. I believe there really only needs to be posited very low entropy prior conditions even, so we may not fall into problems with time/spacetime at the initial big bang. I think Conifold was being very charitable. I kind of meant that time can be its own concept and without inherent direction if prior geometry explains observed directionality.
    – J Kusin
    May 13, 2023 at 1:09
  • By using the words "initial" and "prior", you seem to be already assuming a direction of time for explaining the direction of time. Also, I haven't kept up with the latest in philosophy since I no longer have access to a university library, but I would think that these arguments are reliant on strong reductionism, which others on this list have said is no longer dominant. What I mean is that although the laws of mechanics may be symmetric with respect to time, lots of other laws in other special sciences are certainly not. May 13, 2023 at 1:09

What he is saying is that if you consider, for example, this answer, it grows on my screen letter-by-letter as I type it. Each letter appears as a result of a cause, namely my finger hitting a key which triggers electronics in my laptop which display the letter an instant later. There seems a natural uni-directional order to the character-by-character growth of my answer. If you consider the sequence in reverse order, you will see characters disappearing from the screen one by one without a cause.

Now, suppose I had taken a video of myself typing my answer, and I send the video to you split in two halves and ask you to work out which half came first. You would see certain characters on the screen in both videos, but some characters in only one. You will know, therefore, that the video which shows more characters must be the later video. Or, to make the matter clearer, suppose I type some characters onto a laptop, then post the laptop to you and you type some characters onto it. The characters I type on the laptop while it is in my possession are also on the laptop while it is in your possession, while the characters you type on the laptop do not appear on the laptop while I have it. There is a fundamental asymmetry that gives a natural directionality to time.

  • Surely the letters are getting sucked back into your fingers..?
    – CriglCragl
    May 12, 2023 at 18:58

In short: Time have two forms natural - circle and artificial - timeline.

The causa is an external viewing outside the process and time, that is why Time have a circle from.

Thou art Time.

But when you are inside the process, without causal=external view point, time is line and you are subjective to power of Time. Time eats you.

Edit one:

About this example. This example is more then about the second law of thermodynamics only. This example is about Time beginning. The problem in this example, that the stone is already "marked" because it is "a stone", and more it is "a throwing stone", and more this is "a throwing stone that We threw".

This is already the condition of causality, the causa for "a throwing stone that We threw" existence. This is already mark "Z"(zero).

But, if you have no this mark, you can't say anything about what is it, where is it, when is it. That is why the causa ≥ then time, space or sign together. Cause art everything.

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