I think this is a fair presentation of Łukasiewicz's view on past, present, and future statements in an answer by Johannes https://philosophy.stackexchange.com/a/31995/29944: "His view is that statements about the past and present have an unalterable truth value, so if they are true they are necessarily true, if they are false they are necessarily false. Future contingents are assigned the value i, those statement are possible."

But if I were to claim Alexander the Great fell off his horse on his 12th birthday, is that statement "necessarily truth" or "necessarily false"? We have no way to know whether Alexander fell off his horse on his 12th birthday. Hence, it's neither true nor false, no different from statements about the future. In BOTH cases we have no way to know, hence BOTH are indeterminate.


3 Answers 3


I’m sure Łukasiewicz’s answer would be that the statement about the past is necessarily true if Alexander did fall off his horse and necessarily false if he did not. That we do not know which happened is not relevant. What matters is whether the state of the world determines the truth value or not. In the case of future contingents, the state of the world at a time sufficiently far in advance does not determine what will happen (Łukasiewicz being an indeterminist). When it happens, or when it becomes inevitable that it will happen, the statement gets a definite truth value. For example, at some point in the future, the earth will be destroyed by the sun becoming a red giant. We don’t know when it will happen, but it is sure to do so. So in this case the statement “The earth will be destroyed by the sun” is true.

On your view, almost all the things that happen in the universe are not known, so if described in a statement, that statement would have truth value ½.

For the record, I happen to think Łukasiewicz is wrong about future contingents. I think statements about the future, provided they are not vague, have a definite truth value. I also think you do not need to be a determinist to hold this view. Two of my heroes, William of Ockham and Jean Buridan, held that future contingents have a definite truth value even though we usually do not know which it is.


That is my point-of-view: unknowable ≡ indeterminate. As a matter of fact, considering the two, unknowable statements about the past and unknown statements about the future, the latter is forever forbidden to us by the laws of physics while the former in simply yet to be revealed. In that sense, to me, the "forever unknowable" is more unquestionably neither/nor and not either/or than the simply "unknown now".

Of course, this assumes unquestionable comes in degrees.

  • Would you have any references you could perhaps quote where the reader could get more information? Those references would also strengthen your answer. Welcome to this SE! Sep 30, 2018 at 8:24
  • I wish I could. These are just some random thoughts that have been rattling around inside my head for quite some time when I happened upon this forum, which gave a means to exorcise them. I'm a software engineer by trade but was smitten by philosophical questions in logic some time ago.
    – jski
    Sep 30, 2018 at 11:52
  • I'll search about to see if others have considered this. I'd be surprised to find I'm the first to consider this.
    – jski
    Oct 1, 2018 at 13:11

The use of a third logical value runs afoul of the principle of the excluded middle. If this principle is to be rejected and a 3-valued logical calculus to be constructed, it would naturally have far broader application to indeterminacy and ambiguity than a narrow consideration of future contingents.

An important technical distinction can be made between a statement having the third value and thus being equivocal or indeterminate in this sense, and a statement being definitely either true or false, but it may not be known which is the case.

  • The point of view I'm trying to convey here is that something that is "forever unknowable" (because we cannot unravel the current state of the universe and infer whether Alexander fell from his horse and the laws of physics forbid us from traveling back in time to observe Alexander's 12th birthday) is practically speaking as indeterminate as any statement regarding the future.
    – jski
    Oct 12, 2018 at 18:38
  • BTW, I've searched the web for any consideration of this point of view. All I could find regarding the truth value of statements about the past is that they're either true or false.
    – jski
    Oct 12, 2018 at 18:42

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