3 min and 55 sec to read, 978 words

As noted in an earlier post, not all statements about the future are necessarily predictions. In that post we explored the idea of a spectrum of future statements, ranging from guesses to prophecy – ordered on some kind of notion of the robustness of the data and process that led to the production of the statement itself. How a statement about the future is produced is one way of evaluating it, and a taxonomy can certainly be built around the means of producing such statements – but are there other ways of approaching this problem as well?

One possibility is to look at the use of the statement – it could look something like this: a guess is offered by someone who has no intention of acting on the statement, a prediction is a statement that the person uttering it intends to use to make decisions, a prophecy is a statement that is intended to force one person’s prediction upon another person or persons. The different use cases for statements about the future are descriptive, decisional and normative – or something along those lines.

In some sense, then, we should value these statements differently – and if we are trying to make our own predictions we should value those statements by others, where they intend to use the statement to make decisions, higher than other kinds of statements about the future. Predictions are statements from someone who has skin in the game, and will need to act on the basis of the statement.

One way to think about this is to say that predictions should always be possible to translate into bets. Guesses and prophecies are at least not intended to be taken that way, and many people would not take a bet based on a guess they made, and would be offended if offered a bet on a prophecy, since the bet suggests that there is some uncertainty lingering in the prophecy.

And that gives us another angle: the uncertainty associated with the statement. And here we might want to think about this as a kind of Knightian uncertainty that is not easily reducible to probabilities – and so we end up with something like this: a guess is made about an event that is more uncertain than not, a prediction can only be made about an event where the uncertainty has been reduced to probability at some acceptable rate and residual uncertainty in the web of causes around the event is largely eliminated and a prophecy is a statement about an event almost without any uncertainty at all.

This ties the statements about the future, in an interesting way, to the events that they are about — the nature of those events determine if we have to do with a guess, prediction or prophecy — if we believe that uncertainty is a property of the event rather than our knowledge about the event (this mirrors the question of subjective probabilities, I think).

Another aspect of the robustness analysis would be to look at how embedded a statement about the future is in our web of belief. A guess, under this taxonomy, is almost disconnected, or just loosely attached to our overall web of belief. A prediction is connected and the more connected it is the deeper we believe it. A prophecy, however, might exist very close to the center of our web of belief and shape us deeply. This approach allows us to see statements about the future as more or less a part of our identity. A guess says very little about a person’s beliefs – a prophecy says quite a lot. This, intriguingly, seems to imply that predictions and prophecies can be used to make predictions about the person making the predictions and their world view.

Predictions should be about the future as well (seems obvious) — even though we do not always use the term that way. We sometimes say that a certain theory predicts a fact, something that eliminates the timeframe. This seems muddled, and the old predictivist debate is interesting here: in short (very short) this is a debate about whether it is right to say that something is predicted or accommodated by a theory. Intuitively it would seem more correct to suggest that a fact or fact pattern can be accommodated within a theory, but a future event predicted by the theory. ¹ See for a write up here: https://plato.stanford.edu/entries/prediction-accommodation/

So, as always, let’s invert. When is a statement about the future absolutely not a prediction, nor a guess or a prophecy? I think the best example of that is probably a statement about the future that expresses a hope. Hope seems to be almost the opposite of a prophecy, something we actively believe will not happen (we would in fact often take a bet to the opposite if we were not so desperately hoping) — or at least something we would not even have guessed would happen.

Hope, then, occupies a counter-factual role in the theory of predictions – a sort of inverse prediction attached to a strong preference for the world to be a way we think it will not turn out to be?

What about absolutely determinist statements about the future that contain no uncertainty at all? Prophecies still have some uncertainty – if only just the uncertainty that comes from a belief not being shared by others – but are there completely determined statements about the future? Perhaps physical laws are the closest we can come to such statements about the future – but they are statements from a point outside of time, in some way. They are statements about the past, present and future of a state space.

A physical law eliminates all space for hope, and physical laws do not predict – but accommodate – timeless facts.

Footnotes and references

• 1
  See for a write up here: https://plato.stanford.edu/entries/prediction-accommodation/ ↩︎