I often use the made-up term "time-travel fallacy" to describe certain poor arguments. I'm wondering two main things:

  • is this an already existing concept, and I just don't know the right name?
  • is it ok to use this term in conversation as long as imply that I made it up?
  • and maybe thirdly, is there anything wrong with this concept as I described it?

The way this kind of mistake arises is from the fact that it is extremely easy for people to imagine two distinct time-frames and argue from both time-frames at once, when they never could have been in a real position to do so.

In a real situation, they either would be in the past time-frame with no knowledge of the future, and no moral obligation to it either, or else they would be in the future time-frame, and the past time-frame would be in the past, and any knowledge gained from hind-sight would be irrelevant as far as decisions made in the past go.

Arguing as if both the earlier time-frame and later time-frame are both a part of the same present is the "time-travel" fallacy. The state of the later time-frame cannot be used to make decisions in the past. One way of describing this is with the phrase "hind-sight is 20-20", but I think that "time-travel fallacy" is a little more broad than that, since "hind-sight" is only one way of making this mistake.

A potentially controversial example that I am hesitant to use since I don't want to get side-tracked by the issue itself is abortion, but it's a good example. (It's not the only example, though.)

A common argument against abortion is to think about the future person that you would be aborting, or to point to existing people and ask whether you would have aborted them. This is the time-travel fallacy, conflating the future with the present, or the present with the past.

A person that exists presently exists presently, and you can't make decisions in the past based on the present. Similarly, a person that does not exist yet, but will in the future, still does not exist in the present, and you can't make decisions in the present based on the inferred state of the (distant) future.

(This is not meant to avoid consequences of actions; if A causes B, and B is bad, then you should avoid doing A, but if A and B are sufficiently removed from each other to the point that B can only be loosely imagined, and the future that B exists in is completely imaginary, then there is no such obligation. The point as far as the abortion thing goes is that you are not "murdering" the future person, because that person does not exist yet. You cannot argue as if the future is the present.)

  • 1
    You need either a better example or a different way of putting your notion of responsibility. Arguments 'for' abortion often consider the future person's likely misery as an unwanted child, arguments against it usually just declare that is already a person, whose death you are causing, and are not involving your 'fallacy'. As it is, I have no real clue what you mean, other than false assignment of effect or cause, and false predictions or false causes can rely upon a range of fallacies, not a single one.
    – user9166
    Oct 8, 2016 at 17:11

1 Answer 1


I believe what you describe is close to what is called anachronism (literally, out of time -ism):

"In historical writing, the most common type of anachronism is the adoption of the political, social or cultural concerns and assumptions of one era to interpret or evaluate the events and actions of another... Arthur Marwick has argued that "a grasp of the fact that past societies are very different from our own, and ... very difficult to get to know" is an essential and fundamental skill of the professional historian; and that "anachronism is still one of the most obvious faults when the unqualified (those expert in other disciplines, perhaps) attempt to do history". Anachronism in academic writing is considered at best embarrassing..."

This is usually used more broadly and on a greater time scale than yours, but in its ethical application the idea is the same: decisions and actions should be judged based on information and context available at the time, not from the all-knowing perspective available with the benefit of hindsight. "No second guessing", "no Monday morning quarter backing" are lower brow expressions of this sentiment.

The OP abortion example puts an additional twist on it, however, and a controversial one. What it seems to argue is, roughly, that abortion is not murder because the "person" in question (fetus) is only a potential person, and therefore does not yet exist. This sentiment is also expressed as "to die is not the same as never to be born". This is a defensible position, but one will have harder time dismissing the opposite one as anachronistic.

There is a well established school of thought which holds that potential existence is also a kind of existence, and it carries moral value with it. In other words, it is not necessary for people to place themselves in two different time frames at once, they can argue from a single time frame, but acknowledge its potentialities in addition to actualities. The device of subjunctive mood and the use of counterfactuals you mention evolved precisely for such purposes. Felt discusses potentiality in the context of free will and responsibility in Impossible Worlds:

The actualists are therefore right in denying an independence to the possible. On the other hand, to be potentially is really a way to be, even though it is not to be actually. And this of course is just what Aristotle said in response to Parmenides, who conceived of only one way of being, being in actuality.

The real issue, as you yourself point out at the end, is how to balance the likelihood of consequences against their utility and/or moral value, and that is the crux of most intractable problems in ethical consequentialism. It would be so much easier if we had a firm grasp and consensus on what is or is not a "sufficiently removed" consequence, and how much of an existence potential existence is. Slippery slope is another kind of situation, whose being or not being a fallacy turns on such judgements.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .