Possibility, Necessity, and Chance
Possibility is a central topic in contemporary and classical metaphysics. It is often taken up along with necessity. Since the two of them represent two modes of existence of an entity, possibility and necessity are also said modalities – to be more exact, they are alethic modalities, that is they are those modalities that pertain to truth and falsity.
In ordinary discourse, possibility is often associated with chance: to say that a certain scenario is possible is to associate some non-zero degree of chance for it to take place. However, philosophically speaking, it is standard to keep the two notions separate. On one hand we have the issue of defining what is it that possible entities are and how we can know about them, on the other we have the issue of assigning a probability to such scenarios taking place. The latter task is often left to some sort of scientific calculation, or to a calculation based on what we have so far observed; whether a scenario is possible or not, however, may be settled in ways that are independent from our past observations.
The Metaphysical Enigma of Possibility
You are reading those words at this time, but it was possible you would have been doing something else right now. This article may have not existed. Or your day may have developed differently. An argument such as this seems plausible, at least prima facie; but, on the basis of what may it be true? That is, take the sentence: "You may have not been reading this sentence at this time" and suppose that it is true: what makes it true? After all, you have been reading the sentence right then: that event took place and so any judgment about its possibly not happening must be based on evidence that is not what was the case.
Judgments of possibility concerning scenarios that run counter to what in fact happens in our world – also called counterfactual scenarios – are quite common. You say a word too many to your friend and immediately think: "Ah, if I would have shut up that would have been better!" Or, your favorite sport team gets very close to win a match, but loses or ties at the very last moment. In each of those circumstances, we may wonder – if the scenario we envisage was really possible, without it having existed, what is such scenario?
The Epistemic Enigma of Possibility
Possibility, however, is an enigma also from an epistemic point of view. If some possible scenarios have never be realized (only a tiny fraction of that which seems possible, indeed, becomes actual), how do we know that they were possible? How do we gather knowledge about possibility?
You may often tell whether a philosopher is an empiricist or a rationalist by looking at how she answers the question raised above. The typical empiricist reply will appeal to past evidence: if you believe that a scenario is possible it is because you have observed scenarios in the past that resembled the one in question. A rationalist will typically be, at least in part, dissatisfied with such an answer: some scenarios that we may deem possible are so far fetched from actual scenarios that our knowledge of them cannot be based on past evidence.
The dispute is alive and kicking. Stay tuned.
Further Online Sources
- The entry on the Epistemology of Modality at the Stanford Encyclopedia of Philosophy.
- The entry on Modal Logic at the Stanford Encyclopedia of Philosophy.
- The entry on Chance vs Randomness at the Stanford Encyclopedia of Philosophy.
- The entry on Modal Metaphysics at the Internet Encyclopedia of Philosophy.